Meditations on First Philosophy (subtitled In which the existence of God and the real distinction of mind and body, are demonstrated), written by René Descartes (1596 - 1650) and first published in 1641, expands upon Descartes' philosophical system, which he first introduced in his Discourse on Method (1637).

The book is made up of 6 meditations, during which Descartes discards all belief that is not absolutely certain, then tries to establish what can be known for sure.

The first meditation reveals four situations which have the potential to distort our perceptions enough to invalidate a series of knowledge claims. The most knowledge invalidating argument Descartes presents is that of the evil deceiver , who has the power to deceive us of all our perceptions and casts doubt on all we can know of the world and the properties it contains. However, even though the deceiver can falsify our perceptions, it does not have the power to falsify what we "seem" to perceive. Descartes also concludes that the powers to think and exist are untouchable by the deceiver.

The second meditation contains Descartes' argument for the certainty of one's own existence, even if all else is in doubt:

I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it 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 ... the proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.

In other words, my consciousness implies my existence. In one of Descartes' replies to objections to the book, he summed this up in the now-famous phrase, I think, therefore I am (or in Latin: cogito ergo sum).

The rest of the book contains arguments that modern philosophers have found less convincing, such as ontological arguments for the existence of God, and the supposed proof of the dualism of mind and matter.

External links

• The Meditations
• Essays about The Meditations