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Outline Descartes’ ‘evil demon’ argument and explain what he says about knowledge of the self.

In the First Meditations, Descartes aims to determine which of his many beliefs amount to knowledge. Descartes argues that if there is any doubt regarding the truth of a proposition, one does not know that proposition. For example, Descartes reflects that although he may appear to know that he is sitting by the fire, the sensory experience of sitting by the fire could be an illusion or a dream. If a sensory experience could be caused by a dream, it is not certain and hence not knowledge. Descartes introduces the idea of an ‘evil demon’ as a device to subject all beliefs to rigorous sceptical doubt. He reasons that a demon intent on deceiving could easily make it appear to Descartes that he is sitting by the fire, even if this was not the case. If Descartes’ sensory experience of sitting by the fire could be caused by an evil demon, Descartes does not know that he is sitting by the fire. It is important to note that Descartes is not suggesting that such a demon exists – the mere possibility of the demon existing suffices to deprive Descartes of knowledge. Since we cannot determine whether we are being deceived by an evil demon, we cannot rule out the evil demon possibility. 

More formally, Descartes’ argument can be structured as:

P1: I know a proposition only if I can rule out the possibility of it being false.

P2: If I am being deceived by an evil demon then all propositions I believe are false.  

C1: Therefore, in order to know a proposition I need to rule out the evil demon possibility.

P3: I cannot rule out the evil deceiver possibility.

2: Therefore, I lack knowledge.

Having established the strict criterion for knowledge as being immune from doubt, Descartes goes on to argue that knowledge of one’s own existence does in fact meet this criterion. For Descartes, we do know that we exist. Knowledge of one’s own existence escapes the sceptical conclusion because if I am being deceived, I must exist in order for there to be an ‘I’ which is deceived. Therefore, “this proposition: I am, I exist, whenever it is uttered from me, or conceived by the mind, necessarily is true" (Meditations on First Philosophy, 1641, Second Mediation §25). In other words, one’s own existence is something that we cannot doubt, even postulating an evil demon, and so amount to knowledge.

[A question like this could appear in Unit 1, section 1 of the Philosophy A level. In answering this exam question, you need to pay careful attention to the wording: are you being asked to outline, explain, evaluate or compare? This question comes in two parts and you must make sure that you have explained both the evil demon argument and how self knowledge evades it. The most important qualities in an A level Philosophy answers are clarity, precision, integration and use of technical language. Structuring the argument is premise-conclusion format helps you be clear and precise. However, you must be careful to explain the premise-conclusion argument in prose as well, showing that you understand the argument and haven’t simply memorised it. Explaining it in prose also allows you to use technical language and integrate the two sections of the question. It can be tempting to write everything you know about Descartes – resist this temptation! Carefully plan your answer and ensure that each paragraph clearly addresses the question.]