8.3
From Metaphysics to Physics to expérience:
Cartesian Empiricism
Descartes more than once remarks that the role of experiment is to provide
demonstrations of the first principles or truths of physics by connecting them to the
way God actually made the world. In Part IV of his Discourse on Method he says:
But I must also admit that the power of nature is so ample and so vast, and the principles
so simple and so general, that I notice hardly any particular effect of which I do not know
at once that it can be deduced from the principles in many different ways; and my greatest
difficulty is usually to discover in which of these ways it depends upon them. I know no other means to discover this than by seeking further observations whose outcomes vary
according to which of these ways provides the correct explanation.49
In Part III, Article 46 of Descartes’ Principles of Philosophy he says:
For, seeing that these parts could have been regulated by God in an infinity of diverse ways; experience alone should teach us which of all these ways He chose. That is why we are nowat liberty to assume anything we please, provided that everything we shall deduce from it
is
{entirely} in conformity with experience.50
The idea is that human reason alone cannot discover how God chose to create the world—for the possible ways that reason can conceive exceed the one actual world that the senses come into contact with. The appeal to experience and observation is what delimits the merely conceivable, possible ways to the actual one, and so plays a necessary role in scientific knowledge. We must appeal to experience in order to
find our way back from effects to their causes.
A similar idea runs throughout Desgabets’ Supplement:
He [Descartes] founds the laws of nature for physics only upon the simple supposition that God, in creating the world, put as much movement in the totality of matter as is found there
at present, which we know from experience: this is sufficient for Descartes to deduce the
formation and nature of all things that make up the visible world, in reasoning always from
the cause to effects with consequences similar to those of mathematics. [author’s
emphasis]51
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