The _form_ of bodies is the relation of their elements to each other _in space_,--the _power_ of bodies is their relation to each other _in time_; and both form and power, if considered separately from the number of elementary corpuscles, and from the changes that arise successively, are equally abstractions of the mind, and nothing more. In a former Lecture, I alluded to the influence of errors with respect to the nature of abstraction, as one of the principal causes that retard the progress of philosophy. We give a name to some common quality of many substances; and we then suppose, that there is in it something real, because we have given it a name, and strive to discover, what that is in itself, which, in itself, has no existence. The example, which I used at that time, was the very striking one, of the _genera_, and _species_, and the whole classes of ascending and descending universals of the schools. I might have found an example, as striking, in those abstractions of form and power, which we are now considering,--abstractions, that have exercised an influence on philosophy, as injurious as the whole series of universals in Porphyry's memorable tree, and one of which, at least, still continues to exercise the same injurious influence, when the tree of Porphyry has been long disregarded, and almost forgotten. In the philosophy of Aristotle, _form_, which all now readily allow to be a mere abstraction of the mind, when considered separately from the figured substance, was regarded as something equally real with matter itself; and indeed, _matter_, which was supposed to derive from _form_ all its qualities, was rather the less important of the two. Of substantial forms, however, long so omnipotent, we now hear, only in those works which record the errors of other ages, as a part of the history of the fallible being, man, or in those higher works of playful ridicule, which convert our very follies into a source of amusement, and find abundant materials, therefore, in what was once the wisdom of the past. Crambé, the young companion of Martinus Scribblerus, we are told, “regretted extremely, that substantial forms, a race of harmless beings, which had lasted for many years, and afforded a comfortable subsistence to many poor philosophers, should be now hunted down like so many wolves, without the possibility of a retreat. He considered that it had gone much harder with them, than with _essences_, which had retired from the schools, into the apothecaries' shops, where some of them had been advanced into the degree of quintessences. He thought there should be a retreat for poor substantial forms among the Gentlemen Ushers at Court, and that there were indeed substantial forms, such as _forms of Prayer_ and _forms of Government_, without which the things themselves could never long subsist.”[27]