Consequently a distinction proceeding on this ground seemed more imperative and more definitive then than is the case to-day.

As a fact in the sequence of development, therefore, the distinction is a substantial one and rests on sufficiently valid and cogent grounds.
The ground on which a discrimination between facts is habitually made changes as the interest from which the facts are habitually viewed changes.

Those features of the facts at hand are salient and substantial upon which the dominant interest of the time throws its light.

Any given ground of distinction will seem insubstantial to any one who habitually apprehends the facts in question from a different point of view and values them for a different purpose.

The habit of distinguishing and classifying the various purposes and directions of activity prevails of necessity always and everywhere; for it is indispensable in reaching a working theory or scheme of life.