Descartes’ Discourse on Method, part 5

1. For a full account of his physical views, D. refers us to The World and the Treatise on Man, both published posthumously because of Galileo’s condemnation, as per letter to Mersenne.
2. The World contains a hypothetical causal account of the formation of the world starting from the laws of motion, themselves derived from God’s perfection.
3. In the Treatise on Man, D. cannot give a causal account of the production of man, and therefore he supposes that God has fashioned a material man with all the organs we have and kindled his heart with a flameless fire, so as to make it alive. Such a man would have all the capabilities and functions of animals because the body is nothing but a machine made by God. The soul is not a precondition for life.
4. However, people are more than machines because:
they can use language creatively (not parrot-like)
they can do well or moderately well in all situations because reason is a universal instrument. By contrast machines can do well in a restricted range of situations. For example, a clock keeps time very well. Hence, from the fact that some animals are very good at one or two tasks (e.g., the spider making the web) we should infer that they are just machines.
the non-machine like part of people is the soul, an immaterial, unextended substance that is naturally immortal.
the soul is in not in the body like a pilot in the ship because it is united to the body so as to have sensations, feelings, and appetites.
by contrast, animals are but machines, lacking not only reason but also consciousness, and therefore sensation, feelings, and appetites as well.

Cartesian physics.

1. the essence of matter is extension (onion peeling procedure).
2. matter is passive: its original motion must come from without (from God, a spirit).
3. God imparts motion to matter. Since God is immutable

• the total quantity of motion (mv) is constant because God maintains it. This idea tied to continual creation.
  
• the passivity of matter leads the the first law of motion: a body remains in its state unless acted upon. That is why a stone keeps moving once it has left the hand.
  
• second law of motion: a moving body, left to itself, moves in a straight line. The reason is that God’s immutability requires that God maintain the body’s motion as it is, and experience shows that bodies fly off along the tangent.

NOTE: D’s laws of impact are famously wrong.

• the fact that no other satisfactory explanation of natural phenomena can be devised.
  
• the fact that natural objects are machines, and therefore can be resolved into the motions and configurations of their parts.
  

Descartes’ achievement.

If successful, Descartes has achieved the following main results:

• the establishment of metaphysical foundations for the new physical sciences. Matter is but extended substance, and hence subject to mathematical treatment on the basis of clear and distinct ideas of size, shape, etc. Consequently, the physical world is like a big clock. This leads Descartes to attempt mechanical explanation of physical phenomena, e.g. the explanation of the magnet.
  
• Matter is passive and put in motion by God. Quantity of motion mv (scalar) is conserved because God is immutable and doesn't change the basic laws of nature.

NOTE: this, however, opens the issue of the conservation of quantity of motion and the possibility of free will.

• the mind has been shown to be a substance independent of matter, and hence naturalism, the view that humans are fully explainable on the basis of the laws of nature, is false.

NOTE: However, tension set up by Descartes' attempt to explain many of the activities of man mechanically: the more this approach is successful, the more one is led to believe it could be extended to the mental.

• There is one extended substance (nature) and a great number of unextended immaterial substances (minds). Minds have free will and are outside of the mechanistic and deterministic material world in spite of interactionism. Hence the new science and traditional religious values (freedom of the will, immortality of the soul, existence of God, etc.) are not only compatible, but closely connected. However, Descartes’ God is more that of natural religion than that of Abraham.