In a nutshell:
Last time on "I think, therefore I am": Descartes planned to destroy his whole "building of knowledge" in order to rebuild it, but this time – standing on a solid, confirmed basis. ,
Photo courtesy of G Travels
Descartes, as explained in the previous post, strived to put his whole body of knowledge to the test, so that he may be sure he doesn't hold any false or non-based beliefs. It is worth remembering that by "belief" I (as did Descartes) refer to a proposition accepted as true; this has nothing to do with "faith", which implies a non-critical acceptance of assumptions.
Descartes compared his whole belief system to a building, which must stand on a very solid basis in order not to collapse. And here is a first exercise, or a first illustration of the difficulty to break apart from all of our accepted beliefs, so as to critically review them: many of us would tend to naturally assume that Descartes is looking for an objective basis. In other words: out of an old thinking-habit, we might expect a system of objective beliefs, which any thinking person would agree is true. This (automatic?) assumption is not necessarily true, of course, and this helps us realize that we are often unaware of assumptions we take to be obvious.
I mentioned the methodical aspect of Descartes' doubt as a central reason which led to the great appreciation for the "cogito" argument ("I think, therefore I am" – originally in Latin: "Cogito, ergo sum"). Descartes starts by announcing that he is unable of critically examining each and every one of his beliefs: it is simply unfeasible. Instead, he divides his beliefs into groups, according to the way in which he acquired them. What does this mean?
"All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wiser not to trust entirely anything by which we have once been deceived". [Meditations on First Philosophy] Descartes starts by evaluating the knowledge he gained through his senses: an immensely vast and varied body of knowledge, including our (automatic?) belief that we live in a physical world, which resembles our perceptions of it; that we are corporeal creatures; that other living things exist, etc.
Is it legitimate to doubt all that? Descartes stops to wonder: how is this different from delusions of the mentally sick? However, we do know that our senses deceive us sometimes; for instance, we imagine some things to be small, when they are in actuality huge – but distant. How can we trust our sensory perception, which we know is sometimes misleading us? Moreover, states Descartes, when we dream, we often mistake our dreams for reality. When we are awake, we seem to know that with (what seems to be?) certainty; but we sometimes feel such false certainty while dreaming, too. In these cases we don't only misperceive sensual stimuli; we make up the stimuli altogether, since there is usually no real origin for our dream-time sensations and perceptions. We don't mistake a monster, for instance, to be big, rather than small; the mistake is in our wrong impression that there even is a monster there.
These considerations push Descartes to doubt all of our senses-originated beliefs altogether, until further investigation. There is no need to worry, though: the Cartesian doubt, as explained, aims at destroying the foundations of the building of knowledge – but only to the purpose of rebuilding it, this time on solid foundations. What should be Descartes' next move? Is he already close to finding a basis for a certain knowledge? Are there any more beliefs that should be doubted? What do you think? ,