We normally think of zombies as flesh-eating soulless automations animated by evil forces or radioactive waste. In philosophy of mind, ‘zombies’ are hypothetical creatures that share all the physical characteristics of human beings – including behaviour – but are entirely devoid of consciousness. This can even extend to sharing neurological and biochemical structures.

Zombies are exactly like us in all physical respects but have no conscious experiences: by definition there is ‘nothing it is like’ to be a zombie. Yet zombies behave like us, and some even spend a lot of time discussing consciousness. This disconcerting fantasy helps to make the problem of phenomenal consciousness vivid, especially as a problem for physicalism.

Few people think zombies actually exist. But many hold they are at least conceivable, and some that they are ‘logically’ or ‘metaphysically’ possible. It is argued that if zombies are so much as a bare possibility, then physicalism is false and some kind of dualism must be accepted. For many philosophers that is the chief importance of the zombie idea. But the idea is also of interest for its presuppositions about the nature of consciousness and how the physical and the phenomenal are related. Use of the zombie idea against physicalism also raises more general questions about relations between imaginability, conceivability, and possibility. Finally, zombies raise epistemological difficulties: they reinstate the ‘other minds’ problem…

Read on at the SEP


Q: What does one behaviorist say to another after sex?

A: That was great for you. How was it for me?



Another direct response to this form of skepticism is behaviourism, which in philosophy is associated with Skinner, Carnap and Ryle. In psychology, behaviourism is the view that all human activities (including inner mental life) are exhaustively described by accounts of behaviour. In philosophy of mind behaviourism is the thesis that when we refer to psychological states we refer to concepts whose meaning is exhausted by descriptions of behaviour. You can read more about behaviourism here and here.

For the behaviourist, there is nothing that exists ‘only in the head’ and no such thing as a private mental life. When we talk about ‘desires’, ‘beliefs’ and so on, all we are ‘really’ doing is describing particular behavioural dispositions.

Advantages of Behaviourism:
1. Overcomes the problem of the ‘private theatre’.
2. Behaviourist accounts of mental life are generalisable and available for all to see.
3. Behaviour can be explained in terms which do not themselves presuppose the mental states that are to be explained.
4. Avoiding circular explanations of behaviour. Skinner charges that since mental activity is a form of behavior (albeit inner), the only non-regressive, non-circular way to explain behavior is to appeal to something non-behavioral. This non-behavioral something is environmental stimuli and an organism’s interactions with, and reinforcement from, the environment.
5. For the behaviourist, the problem of other minds does not emerge.

Problems with Behaviourism:
1. Some mental descriptions do not seem to be reducible to behavioural dispositions.
2. Behaviourists seem committed to the belief that there are no mental entities whatsoever.
3. The behaviourist cannot appeal to his own mental experience to understand his mental state—he needs the empirical data of his behavior to inform him of what his mental state actually was.
4. Behaviourism understands the mind as a passive entity which only reacts to its environment.
5. When we talk about pain, do we simply mean ‘pain-behaviour’? What about if we pretend to be in pain?

This argument against skepticism about other minds is often credited to Mill.

‘I conclude that other human beings have feelings like me because, first, they have bodies like me, which I know in my own case, to be the antecedent condition of feelings; and because secondly, they exhibit the acts, and other outward signs, which in my own case I know from experience to be caused by feelings…In the case of other human beings I have the evidence of my senses for the first and last links of the series, but not for the intermediate link…In my own case I know that the first link produces the last through the intermediate link, and could not produce it without. Experience, therefore, obliges me to conclude that there must be an intermediate link; which must either be the same in others as in myself, or a different one; I must either believe them to be alive, or to be automatons; and by believing them to be alive, that is, by supposing the link to be of the same nature as in the case of which I have experience… I bring other human beings, as phenomena, under the same generalizations which I know by experience to be the true story of my own existence’.

(‘An examination of Sir William Hamilton’s Philosophy’, quoted in Hospers p.177)

We can break down his argument in the following way:

1.) Other people have bodies.

2.) These bodies behave as if they had feelings.

3.) In myself, these actions result from feelings, emotions and motivations.

Therefore I can reasonably generalise that:

4.) Other beings have a psychological life like my own.

Mill’s argument might seem compelling, and certainly reflect the way in which we experience other minds indirectly. But why can’t I successfully infer that you have feelings and mental states like mine?

Firstly, unlike a scientific inference, this cannot be tested or repeated in order to guarantee the reasonability of the inference. Maybe you are just a unique creature whose mind is unlike those of others, but shares behavioural traits and physical similarities. If this is the case, the appearance of similarity is no indication of actual similarity. Furthermore, if we accept a broadly Cartesian model of consciousness (as Mill seems to) then we also seem to accept that there is no necessary causal connection between the mind and the body. To work from this observational / inferential basis is to treat others as collections of phenomena, not as ‘people’.

The ‘Problem of Other Minds’ is an epistemological problem.

It is based on the difference between the way we experience our own selves and the way we experience the selves of others. Consider the kinds of mental states that we have ourselves such as beliefs, desires, emotions and feelings.We have direct access to these for ourselves and not for others, but we nonetheless believe that others have these states. Thus, the skeptical objection arises: for the skeptic, we have no epistemological basis for the kinds of knowledge claim that this involves.

We do not really doubt that other people have minds on a day-to-day basis, but the philosophically interesting question arises from the fact that we are not able to justify this belief. Why don’t we entertain thoughts of solipsism? Solipsism (from the Latin ipse = “self” and solus = “alone”) is an extreme form of skepticism, saying that nothing exists beyond oneself and one’s immediate experiences. More generally, it is the epistemological belief that one’s self is the only thing that can be known with certainty and verified (sometimes called egoism).We can understand this philosophical problem as arising from Descartes’ theory of consciousness. The cogito that he advances as the indutiable foundation of truth is a solitary consciousness, res cogitans. For Descartes – as for Berkeley – the external world and other minds are ultimately known only through the benevolence of God, but if we find this argument weak then how can we escape the solipsistic trap of Cartesian skepticism?

It can be contended that empiricist philosophers who accept a broadly Cartesian account of consciousness run the risk of solipsism if they cannot find a way to justify belief in the minds of others.

Like Heidegger, Wittgenstein wants to show that scepticism about the external world does not make sense. How does he go about this?

It is important to note that Wittgenstein is unusual among philosophers in having presented two significantly different philosophies (referred to as ‘early’ (Tractatus Logico-Philosophicus, the only book published in his lifetime) and ‘late’ Wittgenstein).One of the most radical characteristics of “later” Wittgenstein is his view of the task of philosophy. The “conventional” view of philosophy, accepted by almost every Western philosopher since Plato, is that the philosopher’s task was to solve a number of seemingly intractable problems using logical analysis (for example, the problem of “free will”, the relationship between “mind” and “matter”, what is “the good” or “the beautiful” and so on). However, Wittgenstein argued in Philosophical Investigations that these “problems” were in fact pseudo-problems that arose from the philosophical misuse of language. We run into confusion when we try to make language do something that it cannot. Some questions/problems simply do not have an answer – and as such they are not truly questions. The true task for philosophy is not to create grand metaphysical systems, but to identify and defuse linguistic confusion “to show the fly the way out of the fly bottle”. Philosophy therefore has a therapeutic aim.

In his early work, Wittgenstein thought that language was supposed to mirror reality. Anything that did not could be regarded as nonsense (E.g. ‘Is there a God?’). He later came to revise this view and argued that language should be best understood within particular contexts of meaning (language games). This gives rise to the dictum “the meaning of language is in its use”.Language games can take many forms: descriptions, stories, jokes, riddles, guesses, translations, etc. Wittgenstein thought that scepticism about the external world was a game of the type that required clarification in order to make it disappear as a problem. All language games, Wittgenstein argued, presuppose a relationship to the world that is not best characterised as a “belief” and therefore not subject to scepticism.‘Knowledge’ of the external world is not something that one is ever taught, or finds out, or proves. It is more like a background against which we come to know other things.For Wittgenstein, the expression of doubt about the external world presupposes that there is something problematic about a situation, but we cannot take the world itself as an object of concern ‘Doubt’ about the external world is never more than hypothetical and as such cannot really be called ‘doubt’ at all.

“The game of doubting itself presupposes certainty.” (On Certainty 315)    

“It would be as if someone were looking for some object in a room; he opens a drawer and doesn’t see it there; then he closes it again, waits, and opens it once more to see if perhaps it isn’t there now, and keeps on like that. He has not learned to look for things… He has not learned the game that we are trying to teach him.” (On Certainty 315)

“[…] the questions that we raise and our doubts depend upon the fact that some propositions are exempt from doubt, are as it were like hinges on which those turn. That is to say, it belongs to the logic of our scientific investigations that certain things are in deed not doubted. But it isn’t that the situation is like this: We just can’t investigate everything, and for that reason we are forced to rest content with assumption. If I want the door to turn, the hinges must stay put.” (On Certainty 341-3)

“A doubt without an end is not even a doubt.” (On Certainty 625)

This BBC documentary provides a useful introduction to Heidegger’s thought.

Heidegger was a student of Husserl, founder of phenomenology. Husserl was a ‘transcendental phenomenologist’ who thought that there was a direct correlation between our experiences and the world around us. As such, conscious experiences (phenomena) could provide a reliable basis for scientific knowledge. Unlike Heidegger, he retained the subject/object distinction and the transcendental ego.In his attempt to reconsider the history of philosophy and emphasize the importance of the question of Being, Heidegger concentrates on how to we can properly understand our own Being existentially through an analysis of what he terms Dasein.

Dasein = ‘there-being’

As part of his ontological project, Heidegger undertakes a reinterpretation of previous Western philosophy. He wants to explain why and how theoretical knowledge came to seem like the most fundamental relation to being. This explanation takes the form of a destructuring (Destruktion) of the philosophical tradition, an interpretive strategy that reveals the fundamental experience of being at the base of previous philosophies, including that of Descartes.For Descartes, the subject is the seat of experience and is ontologically prior to the world around it . Contrary to this, Heidegger’s goal is to show that there is no subject distinct from the external world of things. Heidegger puts together the separation of the subject and the object by the concept of “Dasein” which is essentially a Being-in-the-world. Being-in, as the most essential and existential characteristics of Dasein, signifies the expression of such terms as “dwelling”, “being familiar with” and “being present to”.

Vorhandenheit [present-at-hand, there]
Zuhandenheit [ready-to-hand, instrumentally available]

For Heidegger, the world is not presented to us as a as a collection of objects that we look upon from a detached perspective, but as a holistic web of interconnected equipment with which we are inextricably entangled. Objects only show up in the context of a background of purposes, concerns, practices and equipmental dealings that is constitutive of our Being-in-the-world. The subject-object perspective is thus a derivative, incomplete understanding, which is blinded by its failure to recognise the primacy of ‘concernful engagement’ with things above traditionally-minded epistemological scrutiny.Theoretical knowledge represents only one kind of intentional behavior, and Heidegger asserts that it is founded on more fundamental modes of behavior, modes of practical engagement with the surrounding world, rather than being their ultimate foundation.Heidegger attempted to unify the duality of modern philosophy by reuniting subject and object (world) together in the single entity Dasein. Subject and object are not two beings, because they are the basic determination of Dasein in the unity of the characteristic of Being-in-the-world. Dasein is not a cogito. Dasein and its world can never be separated. Dasein is the Being-in-the-world. Therefore, “Being-in-the-world” precedes the Cogito. The truth of Cogito is replaced in the disclosedness of Being which is basically primordial truth. Unlike Descartes and others, he breaks the chain of the tradition in terms of an understanding of world. His understanding of Being is Being-in-the-world, but the world of the Being of Dasein is not the physical world. It is the world of Dasein.If we follow Heidegger’s train of thought, we cannot indulge in the kind of skepticism that Descartes presents, since it is predicated on a false distinction between us and the world.

Transcendental Idealism differs from standard (empirical) idealism in that it does not claim that the objects of our experiences would be in any sense only within our minds. Whenever we experience something, that experience is necessarily personal. The object experienced exists independent of our minds, but our perception of it is corrupted by the categories and the forms of sensation, space, and time, which we use to understand it.

In modern philosophy, Kant gave transcendental a new, third meaning in his theory of knowledge, concerned with the conditions of possibility of knowledge itself. For him it meant knowledge about our cognitive faculty with regard to how objects are possible a priori. Something is transcendental if it plays a role in the way in which the mind “constitutes” objects and makes it possible for us to experience them as objects in the first place. Ordinary knowledge is knowledge of objects; transcendental knowledge is knowledge of how it is possible for us to experience those objects as objects. This is based on Kant’s acceptance of David Hume’s argument that certain general features of objects (e.g. persistence, causal relationships) cannot derive from the sense impressions we have of them. Kant argues that the mind must contribute those features and make it possible for us to experience objects as objects. In the central part of his Critique of Pure Reason, the “Transcendental Deduction of the Categories”, Kant argues for a deep interconnection between the ability to have self-consciousness and the ability to experience a world of objects. Through a process of synthesis, the mind generates both the structure of objects and its own unity. For Kant, the “transcendent”, as opposed to the “transcendental”, is that which lies beyond what our faculty of knowledge can legitimately know. Hegel’s counter-argument to Kant was that to know a boundary is also to be aware of what it bounds and as such what lies beyond it — in other words, to have already transcended it.

For Kant, we cannot be skeptical about the (phenomenal) external world since we can establish the necessity of its existence transcendentally.

In what way is Kant’s ‘transcendental idealism dependent on ‘things-in themselves’? What problems are there with the doctrine of things in themselves? How might Kant defend this doctrine?

How can we tell when we are dreaming? Some people have such lucid, everyday dreams that they believe they are awake. When they are truly awake, however, they realize their mistake… how?

Is it possible that you are nothing more than a brain in a vat, cleverly linked up to a machine that stimulates your brain in such a way as to make you believe that you are a person with a body who can walk around, talk to other people and do all of the other things that you think you do every day?

Kant, like Descartes and Berkeley, asks the following question: how can we distinguish appearances from reality? Rationalists (like Descartes) tried to escape the epistemological confines of the mind by constructing knowledge of the external world, the self, the soul, God, ethics, and science out of the simplest, indubitable ideas possessed innately by the mind while Empiricists (like Berkeley) argued that human knowledge originates in our sensations. Kant’s great achievement was to show a way of overcoming this apparently irreconcilable divide. He does this by concentrating on the ‘transcendental structure’of experience.In Kant’s terms, something transcendental relates to the conditions of the possibility of experience: what must be the case for an experience of any sort to be possible at all. He takes ‘time’ and ‘space’ to be structures of this sort. These are not something that we learn from experience, and they are not something we can arrive at analytically through a priori reflection: they are the structures of conscious perception that underlying experience as such. Kant calls these innate structures of intuition the ‘forms of our sensibility’.

“My idealism concerns not the existence of things (the doubting of which, however, constitutes idealism in the ordinary sense), since it never came into my head to doubt it, but it concerns the sensuous representation of things, to which space and time especially belong. Of these [viz., space and time], consequently of all appearances in general, I have only shown, that they are neither things (but mere modes of representation), nor determinations belonging to things in themselves. But the word “transcendental,” which with me means a reference of our cognition, i.e., not to things, but only to the cognitive faculty, was meant to obviate this misconception. Yet rather than give further occasion to it by this word, I now retract it, and desire this idealism of mine to be called critical. But if it be really an objectionable idealism to convert actual things (not appearances) into mere representations… by what name shall we call him who conversely changes mere representations to things? It may, I think, be called “dreaming idealism,” in contradistinction to the former, which may be called “visionary,” both of which are to be refuted by my transcendental, or, better, critical idealism.” 

Kant, Prolegomena to any Future Metaphysics (Remark III)

Another way to understand Kant’s point here is that it is impossible for us to have any experience of objects that are not in time and space. Furthermore, space and time themselves cannot be perceived directly, so they must be the form by which experience of objects is had. The radical part of Kant’s epistemology was the suggestion that, rather than simply be a report on the outside world, the information we receive from our senses are organised by the faculties of the mind into a form that we can make sense of. This is an idea we are quite familiar with in modern times, but Kant was the first to advocate it.

“The solution of this difficulty rests on something that could have been very easily understood from the general bearing of the work, if the reader had only desired to do so. Space and time, together with all that they contain, are not things nor qualities in themselves, but belong merely to the appearances of the latter: up to this point I am one in confession with the above idealists. But these, and amongst them more particularly Berkeley, regarded space as a mere empirical presentation that, like the phenomenon it contains, is only known to us by means of experience or perception, together with its determinations. I, on the contrary, prove in the first place, that space (and also time, which Berkeley did not consider) and all its determinations a priori, can be known by us, because, no less than time, it inheres in our sensibility as a pure form before all perception or experience and makes all intuition of the same, and therefore all its phenomena, possible. It follows from this, that as truth rests on universal and necessary laws as its criteria, experience, according to Berkeley, can have no criteria of truth, because its phenomena (according to him) have nothing a priori at their foundation; whence it follows, that they are nothing but sheer illusion; whereas with us, space and time (in conjunction with the pure conceptions of the understanding) prescribe their law to all possible experience a priori, and at the same time afford the certain criterion for distinguishing truth from illusion therein. “My so-called (properly critical) Idealism is of quite a special character, in that it subverts the ordinary idealism, and that through it all cognition a priori, even that of geometry, first receives objective reality, which, without my demonstrated ideality of space and time, could not be maintained by the most zealous realists. This being the state of the case, I could have wished, in order to avoid all misunderstanding, to have named this conception of mine otherwise, but to alter it altogether was impossible. It may be permitted me however, in future, as has been above intimated, to term it the formal, or better still, the critical Idealism, to distinguish it from the dogmatic Idealism of Berkeley, and from the skeptical Idealism of Descartes.” 

Kant, Prolegomena to any Future Metaphysics (On A Specimen Of A Judgment Of The Critique Prior To Its Examination)

It should be pointed out that Kant is not endorsing the same kind of idealism about objects as Berkeley. That is, Kant does not believe that external material objects are unknowable or impossible. While Kant is a transcendental idealist – he believes the nature of objects as they are in themselves is unknowable to us – knowledge of appearances is nevertheless possible. Kant argues that the ordinary self-consciousness that Berkeley and Descartes would grant implies “the existence of objects in space outside me” (Kant, Critique of Pure Reason § B 275). Consciousness of myself would not be possible if I were not able to make determinant judgments about objects that exist outside of me and have states that are independent of the of my inner experience. Another way to put the point is to say that the fact that the mind of the knower makes the a priori contribution does not mean that space and time or the categories are mere figments of the imagination. Kant is an empirical realist about the world we experience; we can know objects as they appear to us. He gives a robust defense of science and the study of the natural world from his argument about the mind’s role in making nature. All discursive, rational beings must conceive of the physical world as spatially and temporally unified, he argues.Complicated stuff! But what does this all mean? Kant argues that skepticism about the external world is valid in so far as that we can never experience the unmediated content of reality (since it is always tempered by the active part of our own sensuous perception). So, for Kant we do not know ‘things-in-themselves’ (noumena) but we know them as far as we experience them (i.e. as phenomena). However, in as far as we experience phenomena, we share a common perception of them which enables us to judgements about the external world which are (universally) valid for all rational beings. This is Kant’s (direct) response to skepticism about the external world.You can find a copy of Kant’s Prolegomena to any Future Metaphysics (1783) where he discusses Descartes and Berkeley directly at http://philosophy.eserver.org/kant-prolegomena.txt. A guide to the text can be found at http://www.sparknotes.com/philosophy/prolegomena/summary.html.

George Berkeley, an anglican Irish bishop, was another of the great philosophers of the early modern period. He was a critic of his predecessors, including Descartes, and advocated a rather extreme form of Idealism.Idealism is the view that everything that exists is either a mind or depends for its existence upon a mind. Berkeley took this as far as arguing that the external world and material objects cannot be considered ‘real’ in any meaningful sense. Berkeley theorised that we cannot know if an object is, we can only know if an object is perceived by a mind. We can’t think or talk about an object’s being. We can only think or talk about an object’s being perceived by someone. We can’t know any ‘real’ object ‘behind’ the object as we perceive it, which ‘causes’ our perceptions. All that we know about an object is our perception of it. Berkeley did not deny the existence of an external world as such, but did argue that it was impossible to have any knowledge of it, since our knowledge is limited to the contents of our own minds, which are ‘internal’ to us. Berkeley does not deny the existence of ordinary objects such as stones, trees, books, and apples. On the contrary, he holds that only an immaterialist account of such objects can avoid skepticism about their existence and nature. What such objects turn out to be, on his account, are bundles or collections of ideas. These ideas or impressions are all we know, and therefore are all that can be said to exist. Our experiences of apples do not represent anything ‘outside’ or external to us.For external objects, Berkeley argued esse est percipi (‘to be is to be percieved’). For minds, on the other hand, esse est percipere (‘to be is to perceive’). Objects that are not being percieved at a particular point in time by any person, Berkeley argues, continue to exist because they are witnessed by the mind of God, which is infinite.Why did Berkeley take such an odd view of the world? He thought that only this kind of ‘immaterialism’ could overcome the kind of skepticism that Descartes suggested could be applied to the external world. You can find Berkeley’s arguments for Empirical Idealism in A Treatise concerning the Principles of Human Knowledge (1710). This book largely seeks to refute the claims made by his contemporary John Locke about the nature of human perception. Whilst, like all the empiricist philosophers, both Locke and Berkeley agreed that there was an outside world, and it was this world which caused the ideas one has within one’s mind; Berkeley attempts to prove that outside world was also composed solely of ideas. Berkeley did this by suggesting that “Ideas can only resemble Ideas” – the mental ideas that we possessed could only resemble other ideas (not physical objects) and thus the external world consisted not of physical form, but rather ideas. This world was given logic and regularity by some other force, which Berkeley does his best to prove is God. You can find a copy of the full text at: http://en.wikisource.org/wiki/A_Treatise_concerning_the_principles_of_human_knowledge.

One of the primary representatives of this kind of skepticism about the external world was René Descartes, who is often regarded as the first modern philosopher for his break with the scholastic, medieval tradition that preceded him. Descartes was a mathematician, and wanted to find a basis for truth that was as reliable as the mathematical truths of geometry. In his famous book, Meditations on First Philosophy he searches for a founding principle upon which a theory of truth can be based in the way that mathematical truths are all based on a smaller set of foundations like calculus. He hoped to establish a sound basis for scientific method and prove that the real source of truth and scientific knowledge was in the mind, and not in the external senses.In order to show that science rested on firm foundations and that these foundations lay in the mind and not the senses, Descartes began by bringing into doubt all the beliefs that come to us from the senses. His aim in these arguments is not really to prove that nothing exists or that it is impossible for us to know if anything exists (he will prove that we can know external objects later), but to show that all our knowledge of these things through the senses is open to doubt. If our scientific knowledge came to us through the senses, we could not even be sure that anything outside of us existed. The obvious implication is that, since we do know that external objects exist, this knowledge cannot come to us through the senses, but through the mind. Commenting on his own method, Descartes remarked:

“Throughout my writings I have made it clear that my method imitates that of the architect. When an architect wants to build a house which is stable on ground where there is a sandy topsoil over underlying rock, or clay, or some other firm base, he begins by digging out a set of trenches from which he removes the sand, and anything resting on or mixed in with the sand, so that he can lay his foundations on firm soil. In the same way, I began by taking everything that was doubtful and throwing it out, like sand …”  

Replies 7, Oeuvres de Descartes, Adam, Charles, and Paul Tannery, (eds.) 1904. Paris: J. Vrin Vol. 7 p.537

So, for Descartes, the doubting even our most everyday beliefs like the external world was a way of ensuring that our general beliefs have a strong epistemological foundation. Descartes uses two famous arguments to open all our knowledge to doubt: the dream argument (It is possible that I am dreaming right now and that all of my perceptions are false), and the evil demon argument (there could exist an evil demon who has it in his power to make us believe in false things, even with respect to mathematical knowledge). The basic idea in each of these is that we never perceive external objects directly, but only through the contents of our own mind, the images the external objects produce in us. Since sense experience never puts us in contact with the objects themselves, but only with mental images, sense perception provides no certainty that there is anything in the external world that corresponds to the images we have in our mind. Contrary to common sense, we have only our impressions of things and not direct experience of things themselves. Thus, Descartes undermines the everyday, common sense that we take for granted: that there is a world which we perceive.

In the Meditations, Descartes shows that we have good reasons to doubt all kinds of experiential knowledge. Descartes argued that, in fact, there is only one thing that cannot be doubted in this way is the existence of the mind which does the doubting. 

“I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist? No: if I convinced myself of something then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.”  

Meditation 2, Oeuvres de Descartes, Adam, Charles, and Paul Tannery, (eds.) 1904. Paris: J. Vrin Vol. 7 p.25

This thought finds its canonical expression in the motto Cogito Ergo Sum or “I am thinking, therefore I am”(Discourse on Method). Once he has arrived at this point in his discourse, Descartes begins to rebuild his picture of the world as a dualism between mind and body. Descartes was the first to clearly identify the mind with consciousness and self-awareness and to distinguish this from the brain, which was the seat of intelligence. Hence, he was the first to formulate the mind/body problem in the form in which it still exists today. The important point for our purposes is that Descartes provides a comprehensive account of the skeptical problem re: the external world.You can find an online copy of the Meditations by Descartes at http://www.wright.edu/cola/descartes/.See http://www.wright.edu/cola/descartes/synopsis.html for Descartes’ own synopsis of the text. Tom Sorrell’s book on Descartes is a good, accessible introduction and can be found in the library.

Bertrand Russell was one of the most well-known of British philosophers of the 20th century.  Here’s what he had to say about Nietzsche in his History of Western Philosophy.

Nietzsche gives his account of the origins of our moral prejudices in Zur Genealogie der Moral (‘On the Genealogy of Morals’).  You can find the whole text online at:  http://www.mala.bc.ca/~johnstoi/Nietzsche/genealogytofc.htm  

 You might be interested in this BBC documentary about Nietzsche…  You can see striking footage of Nietzsche on his death-bed on my other website at http://blackthumb.wordpress.com/2007/02/19/last-days-of-friedrich-nietzsche/ 

May I be forgiven the discovery that all moral philosophy hitherto has been boring – and that ‘virtue’ has in my eyes been harmed by nothing more than…by this boringness of its advocates; in saying which, however I should not want to overlook their general utility. It is important that as few people as possible should think about morality as interesting – consequently it is very important that morality should not one day become interesting!… Consider for example… the English utilitarians…No new idea, no subtle expression… they all want English morality to prevail: inasmuch as mankind…or the ‘happiness of the greatest number’, no! the happiness of England would be best served; they would like with all their might to prove…that to strive after English happiness…is at the same time the true path of virtue… on earth…They are a modest and thoroughly mediocre species of man, these English utilitarians, [but insofar] as they are also boring one cannot think highly enough of their utility. One ought even to encourage them.

Beyond Good and Evil § 228

A word now against Kant as a moralist. A virtue must be our invention; it must spring out of our personal need and defense. In every other case it is a source of danger. That which does not belong to our life menaces it; a virtue which has its roots in mere respect for the concept of “virtue,” as Kant would have it, is pernicious. “Virtue,” “duty,” “good for its own sake,” goodness grounded upon impersonality or a notion of universal validity — these are all chimeras, and in them one finds only an expression of the decay, the last collapse of life, the Chinese spirit of Konigsberg. Quite the contrary is demanded by the most profound laws of self-preservation and of growth: to wit, that every man find his own virtue, his own categorical imperative. A nation goes to pieces when it confounds its duty with the general concept of duty. Nothing works a more complete and penetrating disaster than every “impersonal” duty, every sacrifice before the Moloch of abstraction. — To think that no one has thought of Kant’s categorical imperative as dangerous to life! …

“Duty”… impersonal and universal – phantom expressions of decline, of the final exhaustion of life… each one of us should devise his own virtue, his own categorical imperative… Kant’s categorical imperative should have been felt as mortally dangerous… What destroys more quickly that to work, to think, to feel without inner necessity, without a deep personal choice… as an automaton of duty? It is a recipe for decadence, even for idiocy…  Kant became an idiot.” 

 The Anti-Christ § 11