The _Institutes of Metaphysics_--the work by which Ferrier's name will descend to posterity--is a development of the Philosophy of Consciousness; but it is more carefully reasoned out and systematised--the result of many years of thoughtful labour. For several years before the work was published (in 1854) the propositions which are contained in it were developed in the course of Ferrier's regular lectures. The _Institutes_, or _Theory of Knowing and Being_, commences with a definition of philosophy as a 'body of reasoned truth,' and states that though there were plenty of dissertations on the subject in existence, there was no philosophy itself--no scheme of demonstrated truth; and this, and not simply a 'contribution' to philosophy was what was now required, and what the writer proposed to give. The divisions into which he separates Philosophy are: first, the Epistemology, or theory of knowledge; secondly, the Agnoiology, or theory of ignorance; and thirdly, the Ontology, or theory of being. The fundamental question is, 'What is the _one_ feature which is identical, invariable, and essential in all the varieties of our knowledge?' The first condition of knowledge is that we should know ourselves, and reason gives certainty to this proposition which is not capable of demonstration, owing to its being itself the starting-point; the counter-proposition, asserting the separate subject and object of knowledge, and the mutual presence of the two without intelligence's being necessarily cognisant of itself, represents general opinion, and the ordinary view of popular psychology. Knowledge, then, Ferrier goes on, always has the self as an essential part of it; it is knowledge-in-union-with-whatever-it-apprehends. The objective part of the object of knowledge, though distinguishable, is not really separable from the subjective or _ego_; both constitute the _unit_ of knowledge--an utterance thoroughly Hegelian in its character, however Ferrier may disclaim a connection with Hegel's system. In space they may be separated, but not in cognition, and this idealism does not for one moment deny the existence of 'external' things, but only says they can have no meaning if out of relation to those which are 'internal'; as Hegel might have put it, they could be known as separable by means of 'abstraction' only. From this point we are led on to the next statement, and a most important statement it is, that matter _per se_ is of necessity absolutely unknowable; or to what Ferrier calls the Theory of Ignorance. Whether or not this theory can make good the title to originality which its author claims for it, there is no doubt that its statement in clear language, such as no one can fail to understand, marks an important era in English speculation. There are, Ferrier says, two sorts of so-called ignorance: one of these is incidental to some minds, but not to all--an ignorance of defect, he puts it--just as we