83. Processes of Definition. Synthesis. Combined Analysis and Synthesis. -- Some sciences are rational, others, exact or experimental sciences, accordingly as their principles are rational or supplied by induction.

The process of definition in the rational sciences is synthetic in the experimental sciences it is first analytic and then synthetic.

(1) Rational sciences. -- By means of ordinary observation we abstract from reality as perceived by the senses certain very simple notions (decomposition) which we then combine into more and more complex objects (synthesis). Each of the notes put into the synthesis is more universal than the object of the synthesis, but their totality is more limited than each of them by itself: synthesis progressively limits its object, and makes its definition (horos horismos).

Example: Three is the first uneven number. Each of the attributes belongs to other numbers; but their combination limits their attribution to the number three: they define it.

As the comprehension of the concept increases, so its extension diminishes. Synthesis, then, is a direct process of definition. We shall see later on that it is at the same time an indirect process of elimination -- of division.

The attribute uneven is opposed to the attribute even; it excludes the number two. The attribute first excludes all the numhers except two and three. So then, the combination, first, uneven excludes all the numbers except three. The definition, first, uneven number, fits the defined object, three, and no other object -- it is adequate.

(2) The experimental sciences end their work with a synthesis: but they begin with an analysis.

To arrive at a definition of life, we begin by observing the various beings which are called living, and look for something in them to justify a common attribute.

When we eliminate in thought that which distinguishes some of the various vital acts from the rest (nutrition; cognitions; appetitive acts, whether sensual or intellectual), we find in them a common characteristic: they are immanent.^{1} Immanent activity is the definition of life.

Division -- elimination of distinctive notes -- has brought us to definition. And definition will bring back again the division from which the analysis began.

Vital immanence is, in fact, found with specific differences in nutrition, in sensations, and in appetitive acts whether sensual or super-sensual. Science descends again front genus to species, from simple to composite.

This alternation of analysis and synthesis, moreover, will be prolonged. Side by side with the forms of immanent activity there are forms of transitive activity; the mind abstracts their common characteristic, activity; this is the generic element, im<

FORMAL CAUSE OF LOGICAL ORDER 63 -->manence is a distinctive note. And the two notes combined form The definition of life, the combination of a notion of kind with a notion of difference.

Thus, through all these species, analysis pursues a genus which is wider and wider, then a type more and more simple, until it arrives at elements not to be analyzed, by means of which those first definitions are formed which are the generating principles of the sciences.

This shows how important is the part played by definition in science. In the experimental or exact sciences, as well as in the rational sciences, to define is to break a thing up and take hold of its simplest determinations, so as to again identify it with these elements (synthesis). The least comprehensive -- and therefore most extensive -- determination is the generic element of the definition; that which complements the generic elements -- which delimits the concept, and hence is peculiar to, and specific of, the thing defined -- is called the specific difference.

Science, however, is in the end always the same: it makes effects known by their causes, consequences by their principles.

{1} See Psychology.