And the most disastrous. Of course, his axiom assumes the truthfulness of its terms. It is impossible to doubt the terms with which one thinks. Therefore truth (which exists) precedes reasoning or thought.
Descartes finds that he has no trouble doubting the existence of real objects/events – our senses too easily deceive us.
Also false. Our senses do not deceive although they can deteriorate. For example, I can look at a fake apple and think it real until I pick it up or feel or taste it. The sense that perceives and makes sense out of the input of the five senses is called in Thomism the "common sense."
The common sense has the following functions:(Regarding these functions, see Aristotle, De anima, III, 2 (426b8-427a15); De somno 2 (455a5). cf: St. Thomas, In de anima III, lect.3, nr. 599 ff.)1. To know all the sensations of the external senses which are known separately by the external senses.
2. To compare and distinguish these qualities, e.g., color and taste.
3. To be aware of the operations of the external senses.
4. To distinguish the real objects from the images of the fantasy, e.g., to know whether we are dreaming, and to realize that our dreams are not reality.
Of course they do, as your example of a fake apple indicates. As you said, they deceive and limit until the deception is exposed. For thousands of years human consciousness perceived and believed that the universe emanated from our local environment. That false belief persisted until we were able to view things from a much more enlightened perspective. It seems foolish to believe that the senses are no longer deceiving us. Ultimate truth is most certainly not how it currently appears to us through the senses.