DISCOURSE ONMETAPHYSICS 599
useful, not only for admiring the artifice of the great Workman, but also in discovering
something useful in physics and medicine. Authors who follow these different routes
should not be hard on each other.
For I see that those who concentrate on explaining the beauty of divine Anatomy
laugh at others who imagine that an apparently fortuitous motion of particular fluids
can make such a beautiful variety of members, and call such people rash and profane,
while on the other hand the latter call the former simple and superstitious like the
ancients who took it that the physicists were impious when they held that it was not
Jupiter that thundered but some matter in the clouds. The best thing would be to unite
both considerations, for, to use a vulgar comparison, the skill of a workman is recog-
nised and praised not only by showing what designs he had when he made the parts of
his machine, but also by explaining the tools he used to make each part, particularly
when these tools are simple and ingeniously contrived. God is skilful enough an artisan
to produce a machine a thousand times still more ingenious than that of our body if that
were possible, using only a few simple enough fluids expressly formed so that only the
ordinary laws of nature are needed to sort them out as necessary to produce such an
admirable effect, but it is also true that this would not happen if God were not the
Author of nature.
I find, nevertheless, that the way of efficient causes is while indeed more pro-
found and in one way more direct and a priori, on the other hand rather difficult when
we get down to details and I think that our Philosophers are most often still rather far
from that. In contrast, the way of final causes is easier and is moreover often helpful in
guessing important and useful truths that would have been a long time in the searching
by the former more physical route, and of this Anatomy can furnish important exam-
ples. I also hold that Snell, the first discoverer of the rules of refraction, would have
taken a long time to find them if he had tried to find out first how light was formed. But
he seems to have followed the method the ancients used in catoptrics, that of final
causes in fact. For, in the search for the easiest way of conducting a ray from one given
point to another by reflection at a given plane (supposing that this is nature’s design),
they discovered the equality of the angles of incidence and reflection, as can be seen in
a little treatise of Heliodorus of Larissa and elsewhere. That is what in my opinion
Snell, and after him (though without knowing anything about him) Fermat, applied
more ingeniously to refraction. For when in the same media the rays observe the same
proportion of sines which is also that of the resistances of the media, it turns out to be
the easiest, or at least the most determinate way of passing from a given point in one
medium to a given point in the other. The demonstration Descartes tried to give of this
same theorem by the way of efficient causes is far from being as good. At least there are
grounds for suspecting that he would never have found it that way if he had not heard
something of Snell’s discovery in Holland.
- RETURNING TOIMMATERIALSUBSTANCES; THEEXPLANATION
OFHOWGODACTS ON THEUNDERSTANDING OFMINDS
AND OFWHETHERWEALWAYSHAV E A NIDEA OFWHATWETHINK
I have found it relevant to insist somewhat on these considerations concerning final
causes, incorporeal natures and an Intelligent Cause in relation to bodies, to make
known their use even in physics and mathematics. On the one hand, this is to purge
the mechanical philosophy of the profanity imputed to it. On the other hand it is to raise