The Cartesian Way of Finding Seed Principles

What follows from the most universal principles of natural things?

Articles 20-43 explain the hypothesis that Descartes used to:

• understand the phenomena of the heavens
• seek out their natural causes.

The best way to understand the nature of Plants or Man is to consider how they gradually come into existence and are generated from their seeds.

This is why we must devise such principles that are the simplest and easiest to know.

From these, we may demonstrate that the stars, the earth, and everything in this visible world, could have arisen as from certain seeds even if we well know that they never did arise from them.

In this way, we shall explain their nature far better than if we were to describe them only as they are now.

We only assign seeds to things in order to get to know their nature more easily.

The principles demonstrate how the following could have arisen:

• the stars and the phenomena of the heavens, as is observed by astronomers
• the things on earth

Earthly Phenomena

Everything that we observe happening above the earth are counted as phenomena of nature.

To discover these causes, the following are the requirements of a good hypothesis.

1. Considered only in itself, it must not imply any contradiction.
2. It must be the simplest that can be.
3. Following from (2), it must be very easy to know.
4. Everything that is observed in the whole of nature must be able to be deduced from it.

We can assume a hypothesis from which we can deduce, as from a cause, the phenomena of nature, even though we well know that they did not arise in that way.

We shall use of the following example.

What is the nature of a parabola that is written on a sheet of paper?

It would make no difference whether:

• that line was first cut from a cone and then imprinted on the paper, or
• that line was described as a result of the motion of two straight lines
• that it arose in some other way, provided that his supposition enabled him to demonstrate all the properties of a parabola.

Even though he may know that it originated from the imprinting of a conic section on the paper, he can nevertheless assume any other cause he pleases that seems to him most convenient for explaining all the properties of a parabola.

So too, in order to explain the features of nature, we can assume any hypothesis we please, provided we deduce from it by mathematical inference all the phenomena of nature.

A more important point is that there is hardly any assumption we can make from which the same effects cannot be deduced-although perhaps with more trouble-from the laws of nature explained previously.

For because, by the operation of those laws, matter assumes successively all the forms of which it is capable, if we consider those forms in due order, we shaIl finally be able to arrive at the form that is the form of this world. So one need fear no error from a false hypothesis.