I. I will reject opinions that are not completely certain using a method of radical doubt.

A. Methodological observation — I do not need to survey each opinion individually, as it will suffice to undermine the common foundations of all my opinions.

II.Three grades of doubt

A. My senses (and memory) are sometimes deceived.

1. Reply — But it would be mad to doubt the senses in ordinary contexts.

B. I sometimes dream I am in ordinary contexts.

1. Reply — But my present experiences are more distinct than when I am dreaming.

a. Rebuttal — But I sometimes dream that my present experiences are more distinct than when I am dreaming.

2. Reply — But the general properties of things that appear in dreams must be real, because they are the raw materials from which dreams are created. E.g., corporeality, extension, shape, quantity, place, and time.

a. Observation — Disciplines that are dependent on composites are doubtful, while disciplines that range over the most simple or abstract things contain something certain.

C. God (or a being of sufficient power) may deceive me even as to general properties as well as mathematical judgments.

1. Reply— But god is good.

a. Rebuttal — But I am deceived at least some of the time, so god's goodness is not incompatible with my being deceived.

2. Reply — But maybe there is no god.

a. Rebuttal — Then it is even more likely that I am always deceived.

3. Difficulty — My credulity keeps returning.

a. Solution — Concentrate on the following hypothesis for the purpose of determining what (if anything) is completely certain:

An evil genius has directed his entire effort at deceiving me.

MEDITATION TWO

I. I return to yesterday's doubts.

A. Question — Isn't there a god (or whatever) over an above me that puts these thoughts in me?

1. Answer — I might be the sole author of these thoughts.

II. Then I must be something.

A. I am not body, as body is dubitable both in the specific case and in general.

B. But I am still something, because if I am being deceived, there must be something to be deceived.

C. Conclusion — "'I am, I exist' is necessarily true every time I utter it or conceive it in my mind."

III. I must still wonder, what am I?

A. I used to believe extremely confidently that I am the mechanism of body.

1. By 'body' I mean a sensible thing with extension that can figure in causal interactions.

2. But, again, body is dubitable.

B. What about thinking?

1. Thought exists. Of that I can be certain.

2. But only over the duration of thought itself.

IV. What else am I?

A. Methodological observation — When I ask this question, I am tempted to use my 'imagination'. (By imagination, Descartes means his faculty of envisioning things.) But that is a suspect method.

B. I can be confident that the procedures involved in this meditation belong to me.

1. I doubt.
2. I understand.
3. I affirm.
4. I will.
5. I imagine.
6. I sense.

V. Corporeal things still seem more compelling than this 'I'. So let us allow ourselves to reflect on corporeal things like this piece of wax.

A. Its tactile and visual properties seem well known.

1. But they change.

a. Does the wax still remain through these changes?

i. Yes.

b. The wax must be the sum total of all the changes it can undergo where extension, flexibility, and mutability remain.

i. I do not know this through imagination because there are more changes than I can conceive.

ii. I perceive what the wax is through the mind alone.

VI. Clear and distinct ideas are achieved through the faculty of judgment alone.

A. I might still be mistaken with respect to the existence or nature of corporeal things.

B. But I can't be mistaken with respect to my apprehension of my own mind.