ENACTMENT: Doubt the reality of everything. Then try to doubt your doubting—doing so actually forces the doubter into existence. Doubting cannot be doubted.
One way to ascertain certain knowledge is to see if a knowledge claim can survive an act of doubt. Anything that is undoubtable has certain existence. Descartes applies this procedure of methodic doubt or “methodological skepticism” to all kind of putative knowing. If there is any way a belief can be undermined, then the knowledge it provides is conceivably false and, so, uncertain.
Descartes applies the method to various types of knowledge—from tradition, from sense experience, and from mathematical construction. If one example from each type fails to survive the test, then the whole class is discounted as dubitable.
- Knowledge from tradition—FAILS, because experts disagree.
- Sense experience—FAILS, because of illusions (refraction, e.g.), hallucinations, and dreams.
- Mathematical knowledge—FAILS, because of errors in calculation (and because we could be tricked by an all-powerful mind manipulator).
The mind manipulator is the toughest obstacle. It could (conceivably) trick us into believing that “2 + 2 = 5” by altering our consciousness as we move through the proposition. Is there any knowing that even the evil demon cannot manipulate?
Well, in the any act of doubting, there is one fact that cannot be doubted—the act of doubting. The act of doubting instantiates doubting, the subject of which (the doubter) must exist. Doubting destroys everything but the doubter. In fact, doubting is positive—it posits the existence of doubting through its very act.
Therefore, the activity of the subject, whether in doubting, cognizing, believing, or willing, is a certainty. And, so, the subject of subjective activity, the recipient and agent of awayness referred to by “I,” has certain existence. The intentional act of doubting establishes the existence of the intentional actor (for as long as intending is enacted).