He discusses the question whether metaphysical axioms are innate.He denies that they are innate in the sense of their being known or observed by the mind from its birth, and affirms that in their general form they are not reached till after many comparisons of singular ideas.He shows that the mind assents to them in their singular form, even when a sensible object is presented.He stands up for axioms, self-evident and immutable, {74} -- with him, as with Locke, self-evidence being their prominent feature and their mark but he also declares them to be eternal and unchangeable, --the mind perceiving at once the agreement or disagreement of the subject or predicate.He denies that there is any principle entitled to be regarded as the first of all, and maintains that it is vain to seek any other criterion of truth than the faculty of reason itself, and the native power of the mind.These views are surely more profound than those of Locke, less extravagant than those of Descartes, Leibnitz, or Wolf (he refers to Wolf).They do not exhaust the subject; in particular, while he says truly (with Aristotle) that the singulars and the less general are first known, he does not enter on the question, which neither the Scottish nor any other metaphysicians have yet settled, of the relation of self-evident truths in their singular to their generalized form.
In regard to space and time, he avoids the extreme positions both of Clarke, who represents them as modes of the divine being, and of Leibnitz, who describes them as mere relations perceived by the mind.He represents them as things or realities, and declares modestly and truly that we are ignorant of the relation in which they stand towards the divine nature.These judicious views were followed by the Scottish metaphysicians generally down to the time of Hamilton.
This leads him into the investigation of the infinite.
He regards the following propositions as probable: that it is scarcely possible that there should be a number of infinite things of the same kind , that the infinite, because it is infinite, cannot be greater; that infinites, so far as infinites, cannot be multiplied; nor can have any finite relation (<rationem>) to finite parts, although things by one reason infinite and by another finite may be divided and multiplied, if only there are other things of the same description.But after enunciating these bold propositions he cautiously adds that these questions may well be held to surpass human capacity.
He declares that, properly speaking, there is only one sort of cause, the efficient.He says that in the impulse and motion of bodies, and in the effort to change the idea in our minds, and to produce motions in our bodily members, we not only see change, but perceive some energy or efficacy.This view is not thoroughly carried out; it certainly is the truth so far as {75} it goes.He cautions us, in the very spirit of Reid, against dogmatizing too minutely as to the power of the mind over the body.
Substance is that which remains when the affections change.He agrees with Locke that the nature of substance is unknown, except that we have an obscure idea of something as the substratum of qualities.His views on this whole subject are meagre and unsatisfactory.
Still it is in the discussion of these questions that he passes beyond Shaftesbury, and shows the clearness, the judiciousness, and the independence of his thinking.I am not sure whether these metaphysical topics have been discussed in a profounder manner by any thinker of the Scottish school except Sir W.Hamilton; and he has not shown the same amount of speculative caution and good sense as Hutcheson.