Describe these figures and present them to external senses

It is also very helpful to describe these figures and present them to external senses, so that by this means our thought may more easily retain attention.

However, how these should be depicted for distinctness, while they are set forth before our eyes, and how their species should be formed in our imagination, is evident by itself.

For firstly, we will depict unity in three ways, namely through a square, if we consider it as both long and broad, or through a line, if we regard it only as long, or finally through a point, if we look at nothing else except what is composed of it in multitude.

But in whatever way it is depicted and conceived, we will always understand it to be the same subject, capable in every way of extension and of infinite dimensions.

In the same way, if attention should be given simultaneously to two different magnitudes of them, we will present them to the eyes through a rectangle, whose two sides will be the two proposed magnitudes.

In this manner, indeed, if they are incommensurable with unity, we will use this, or this, if they are commensurable; and the question will be only about the multitude of units.

Finally, if attention should be given only to one of these magnitudes, we will depict it either through a rectangle, whose one side is the proposed magnitude and the other side is unity, which happens whenever it is to be compared with any surface; or through length alone, in this way, if it is considered only as an incommensurable length; or in this way, if it is multitude.