Meditations on First Philosophy

1. Demolish All Former Beliefs Through Radical Doubt

Hence I saw that at some stage in my life the whole structure would have to be utterly demolished, and that I should have to begin again from the bottom up if I wished to construct something lasting and unshakeable in the sciences.

The Project. To build a foundation of certain knowledge, I must first clear away everything I previously believed. This isn't about proving everything false, but about finding a reason, however slight, to doubt each belief. If the foundation is shaky, the whole structure of knowledge is unstable.

Levels of Doubt. I start with the senses, which sometimes deceive us, especially about distant or small objects. But surely I can trust my senses about things right in front of me, like being awake and sitting by the fire? This leads to the dream hypothesis: perhaps my vivid experiences are just illusions like those in dreams, and there's no certain way to distinguish waking from sleeping.

The Evil Genius. Even if some simple truths, like those of mathematics (2+3=5), seem certain whether I'm dreaming or not, I can still doubt them. What if an all-powerful, evil spirit is constantly deceiving me about everything, including these seemingly obvious truths? To protect myself from error, I will assume that everything I previously believed is false and imaginary.

2. Discover the Unshakeable Certainty of Your Own Existence

So that, having weighed all these considerations sufficiently and more than sufficiently, I can finally decide that this proposition, ‘I am, I exist’, whenever it is uttered by me, or conceived in the mind, is necessarily true.

The Turning Point. After plunging into a whirlpool of doubt, supposing everything I perceive or imagine is false, I find one thing that resists doubt. Even if an evil genius is deceiving me about everything else, I must exist in order to be deceived. The very act of doubting proves my existence.

"I think, therefore I am." This famous insight means that as long as I am thinking (in any form – doubting, understanding, willing, sensing), I can be certain that I exist. This is the first, most certain, and unshakeable truth I can find.

Beyond Imagination. This certainty of my existence does not depend on any bodily thing or sense perception, as those might be illusions. My knowledge of my existence comes purely from the fact that I am thinking.

3. Realize Your Essential Nature is Pure Thought

I am therefore, speaking precisely, only a thinking thing, that is, a mind, or a soul, or an intellect, or a reason—words the meaning of which was previously unknown to me.

What am I? Having established that I exist because I think, I investigate what this "I" is. I previously thought I was a human being with a body and a soul responsible for various functions like nutrition, motion, sensation, and thought.

Stripping Away Doubtful Attributes. Under the radical doubt, I've supposed I have no body, and therefore no functions dependent on a body like nutrition, motion, or sensation (as it relies on sense organs). The only attribute that remains inseparable from me is thinking.

A Thinking Thing. Therefore, my essence, what I am in the strict sense, is purely a thinking thing. This means I am a substance whose whole nature or essence is just to think. This knowledge of myself as a thinking thing is clearer and more certain than any knowledge I have of bodily things, even the wax I examine.

4. Establish Clear and Distinct Perception as the Criterion of Truth

And therefore I seem already to be able to lay down, as a general rule, that everything I very clearly and distinctly perceive is true.

Seeking a Rule. Having found certainty in my own existence as a thinking thing, I examine what made this truth so certain. It was the clarity and distinctness of my perception of it. This suggests a general rule: whatever I perceive very clearly and distinctly must be true.

Testing the Rule. I recall past beliefs, like those about sensible things (earth, sky), which I once thought certain but later doubted. My perception of them was not truly clear and distinct; it was confused, mixing ideas with the assumption that external things caused them and were like them.

The Doubt Lingers. Even mathematical truths, like 2+3=5, which seem clear, could be doubted if I suppose a deceiving God exists. Until I resolve the question of God's existence and nature, this criterion of truth remains vulnerable to the evil genius hypothesis.

5. Prove God Exists from the Objective Reality of His Idea

But now it is manifest by the natural light that there must be at least as much reality in the total and efficient cause as in its effect.

Ideas and Reality. I categorize my ideas: innate (from my nature), adventitious (from outside), and factitious (invented). Ideas represent things, and the reality contained in an idea (objective reality) must have a cause with at least as much reality (formal or eminent) as the idea represents.

Degrees of Reality. Substances have more reality than modes (attributes). An infinite substance has more reality than a finite substance. My idea of God represents an infinite, perfect substance, containing immense objective reality.

The Cause of the Idea. My own finite being cannot be the cause of the idea of an infinite, perfect being, as I do not possess infinite reality formally or eminently. Therefore, the cause of this idea must be an actually existing infinite, perfect being – God.

6. Prove God Exists from Your Own Dependent Existence

For since all the time of a life can be divided into innumerable parts, of which each particular one in no way depends on the rest, it does not follow from the fact that I existed not long ago that I have to exist now, unless some cause, so to speak, creates me again at this moment, or in other words, conserves me in being.

My Existence Needs a Cause. I am a thinking thing, but I am finite and imperfect (I doubt, I desire). I could not have given myself existence, because if I had, I would have given myself all perfections and would be God.

Conservation is Creation. My existence from one moment to the next requires the same power as would be needed to create me from nothing. I have no power to conserve myself; if I did, I would be aware of it.

The Infinite Cause. Therefore, I depend on a cause for my continued existence. This cause must be a thinking thing, and must possess the idea of all the perfections I attribute to God. Tracing this causal chain back, we must arrive at a first cause that exists of itself. This being must be God, possessing all perfections.

7. Understand Error as a Misuse of Free Will

The privation in which the essence of error consists lies in this wrong use of free choice.

The Problem of Error. If I am created by a perfect, non-deceiving God, how is it possible for me to make mistakes? Error is not a positive reality, but a deficiency or privation of knowledge that should be in me.

Two Faculties. Error arises from the interplay of my intellect (faculty of knowing) and my will (faculty of choosing/judging). The intellect is limited; it does not clearly perceive everything. The will, however, is boundless; it can affirm or deny anything, even what the intellect does not clearly grasp.

The Wrong Use. Error occurs when I use my free will to pass judgement on matters that my intellect does not clearly and distinctly perceive. If I restrict my will to affirming only what is clearly and distinctly understood, I will avoid error. God is not responsible for my errors; they result from my failure to properly use the faculties he gave me.

8. Prove God Exists from His Necessary Nature

And I clearly and distinctly understand that eternal existence belongs to his nature—just as clearly and distinctly as I understand that the properties I can demonstrate of some shape or number belong in fact to the nature of that shape or number.

Essence and Existence. I find in my mind the idea of God, a supremely perfect being. Just as the idea of a triangle necessarily includes having three angles equal to two right angles, the idea of a supremely perfect being necessarily includes existence.

Existence as a Perfection. Existence is a perfection. A being that exists is more perfect than one that does not. Since God is supremely perfect, he must possess all perfections, including existence.

Necessary Existence. Unlike other things whose existence is merely possible or contingent, God's existence is necessary. I cannot conceive of a supremely perfect being that lacks existence; the idea is contradictory, like a mountain without a valley. Therefore, from the very idea of God, I can conclude with certainty that he exists.

9. Grasp the Purely Extended Essence of Material Things

I can certainly distinctly imagine the quantity that philosophers commonly call ‘continuous’: that is, the extension of this quantity (or rather, of the thing to which the quantity is attributed) in length, breadth, and depth.

What is Body? Before proving that material things exist, I examine my idea of them. The clear and distinct idea I have of material things is purely of extension in three dimensions (length, breadth, depth), along with modes like shape, size, position, and motion.

Imagination vs. Intellection. My ability to imagine bodily things, like a triangle or a pentagon, seems to suggest they exist. However, imagination is distinct from pure intellection. I can understand a thousand-sided figure (chiliogon) without being able to distinctly imagine all its sides. Imagination seems to involve applying the mind to a body, suggesting dependence on something external.

Mathematical Essence. The properties I clearly and distinctly perceive in the idea of body are those studied in pure mathematics. These are the true, immutable, and eternal essences of material things, independent of whether they actually exist.

10. Prove Material Things Actually Exist Based on God's Veracity

But because God is no deceiver, it is altogether plain that he does not transmit these ideas to me immediately, or by the intermediary of some creature, in whom their objective reality is contained not formally but only eminently.

From Idea to Existence. I have a passive faculty of sensation, receiving ideas of sensible things. This requires an active cause to produce these ideas. This cause cannot be me, as the ideas are involuntary and non-intellectual.

The Cause is External. The cause must be a substance distinct from me, containing the reality of these ideas either formally (actually) or eminently (in a higher form). This substance is either body, containing the reality formally, or God (or a nobler creature), containing it eminently.

God's Guarantee. I have a strong natural inclination to believe these ideas come from actual bodily things. If they came from God or another source eminently, and not from bodies, God would be a deceiver for giving me this strong inclination without providing a way to know the truth. Since God is not a deceiver, bodily things must exist.

11. Establish the Real Distinction Between Mind and Body

And since I know that whatever I clearly and distinctly understand can be produced by God such as I understand it to be, then if I can clearly and distinctly understand one thing without another, this is sufficient for me to be certain that the one is distinct from the other, since they can at least be produced separately by God.

Distinct Concepts. I have a clear and distinct idea of myself as a thinking, non-extended thing (mind). I also have a clear and distinct idea of body as an extended, non-thinking thing.

Separability by God. Since I can clearly and distinctly understand these two substances (mind and body) separately, God can produce them separately. This is sufficient proof that they are really distinct substances.

Indivisibility of Mind. Furthermore, the body is by its nature divisible into parts, whereas the mind, as a thinking thing, is completely indivisible. This fundamental difference in nature further confirms their real distinction.

12. Re-evaluate the Limited but Useful Reliability of the Senses

For, from the fact that God is not a deceiver, it follows inescapably that in such cases I am not deceived.

Senses are for Survival. My senses, like pain, hunger, and perceptions of external qualities, are given by nature primarily to indicate what is beneficial or harmful to the composite of mind and body. For this purpose, they are generally reliable.

Source of Error. Errors arise when I misuse sensory perceptions, treating them as reliable guides to the true essence of external bodies, which they represent only obscurely and confusedly. Errors also occur when the body's natural mechanisms are disordered (like thirst in dropsy).

Distinguishing Waking from Dreaming. Now that I know God exists and is not a deceiver, I can trust the natural signs that distinguish waking from dreaming. Waking experiences are coherent and connected by memory, unlike dreams.

Limited Trust. While senses can still deceive about the precise nature of external things, I can trust them in conjunction with memory and intellect for practical life and to confirm the existence of the external world. The hyperbolic doubts can now be dismissed.

Last updated: May 14, 2025