2: The Migrating Instances

2. The Migrating instance

²³ In these, the required nature passes toward generation, having no previous existence, or toward corruption, having first existed.

In each of these divisions, the instances are always twofold. Or rather, it is one instance:

• first in motion or on its passage, and then
• brought to the opposite conclusion.

These instances:

• hasten and confirm exclusion
• reduce affirmation, or the form itself, to a narrow compass

for the form must be something conferred by this[162] migration, or, on the contrary, removed and destroyed by it; and although all exclusion advances affirmation, yet this takes place more directly in the same than in different subjects; but if the form (as it is quite clear from what has been advanced) exhibit itself in one subject, it leads to all.

The more simple the migration is, the more valuable is the instance.

These migrating instances are, moreover, very useful in practice, for since they manifest the form, coupled with that which causes or destroys it, they point out the right practice in some subjects, and thence there is an easy transition to those with which they are most allied.

There is, however, a degree of danger which demands caution, namely, lest they should refer the form too much to its efficient cause, and imbue, or at least tinge, the understanding with a false notion of the form from the appearance of such cause, which is never more than a vehicle or conveyance of the form.

This may easily be remedied by a proper application of exclusion.

The following is an example of a migrating instance.

Let whiteness be the required nature. An instance which passes toward generation is glass in its entire and in its powdered state, or water in its natural state, and when agitated to froth; for glass when entire, and water in its natural state, are transparent and not white, but powdered glass and the froth of water are white and not transparent.

What happened to the glass or water in the course of this migration?

• The form of whiteness is conveyed and introduced by:
  • the bruising of the glass and
  • the agitation of the water
• But only the following have been introduced:
  • a diminishing of the parts of the glass and water and
  • the insertion of air.

Yet this is not progress toward discovering[163] the form of whiteness, namely, that two bodies, in themselves more or less transparent (as air and water, or air and glass), when brought into contact in minute portions, exhibit whiteness from the unequal refraction of the rays of light.

But here we must also give an example of the danger and caution of which we spoke;

We might think that:

• air is always necessary for producing the form of whiteness, or
• whiteness is only generated by transparent bodies

These are both false.

In fact, all all bodies which are even in such of their parts as affect the sight exhibit transparency, those which are uneven and of simple texture whiteness, those which are uneven and of compound but regular texture all the other colors except black, but those which are uneven and of a compound irregular and confused texture exhibit blackness.

An example has been given, therefore, of an instance migrating toward generation in the required nature of whiteness. An instance migrating toward corruption in the same nature is that of dissolving froth or snow, for they lose their whiteness and assume the transparency of water in its pure state without air.

Nor should we by any means omit to state, that under migrating instances we must comprehend not only those which pass toward generation and destruction, but also those which pass toward increase or decrease, for they, too, assist in the discovery of the form, as is clear from our definition of a form and the Table of Degrees. Hence paper, which is white when dry, is less white when moistened (from the exclusion of air and admission of water), and tends more to[164] transparency. The reason is the same as in the above instances.[110]