In attempting to give some idea of philosophy as it was in Scotland in the earlier portion of the present century, we shall have to go back two hundred years or thereabout, in order to find a satisfactory basis from which to start. For philosophy, as no one realised more than Ferrier, is no arbitrary succession of systems following one upon another as their propounders might decree; it is a development in the truest and highest significance of that word. It means the gradual working out of the questions which reason sets to be answered; and though it seems as if we had sometimes to turn our faces backwards, and to revert to systems of bygone days, we always find, when we look more closely, that in our onward course we have merely dropped some thread in our web, the recovery of which is requisite in order that it may be duly taken up and woven with the rest. At the time of which we write the so-called 'Scottish School' of Reid, Stewart, and Beattie reigned supreme in orthodox Scotland; it had undisputed power in the Universities, and besides this obtained a very reputable place in the estimation of Europe, and more especially of France. As it was this school more especially that Ferrier spent much of his time in combating, it is its history and place that we wish shortly to describe. To do so, however, it is needful to go back to its real founder, Locke, in order that its point of view may fairly be set forth. In applying his mind to the views of Locke, the ordinary man finds himself arriving at very commonplace and well-accustomed conceptions. Locke, indeed, may reasonably be said to represent the ideas of common, everyday life. The ordinary man does not question the reality of things, he accepts it without asking any questions, and bases his theories--scientific or otherwise--upon this implied reality. Locke worked out the theory which had been propounded by Lord Bacon, that knowledge is obtained by the observation of facts which are implicitly accepted as realities; and what, it was asked, could be more self-evident and sane? It is easy to conceive a number of perceiving minds upon the one hand, ready to take up perceptions of an outside material substance upon the other. The mind may be considered as a piece of white paper--a _tabula rasa_, as it was called--on which external things may make what impression they will, and knowledge is apparently explained at once. But though Locke certainly succeeded in making these terms the common coin of ordinary life, difficulties crop up when we come to examine them more closely. After all, it is evident, the only knowledge our mind can have is a knowledge of its own ideas--ideas which are, of course, caused by something which is outside, or at least, as Locke would say, by its _quality_. Now, from this it would appear that these 'ideas' after all come between the mind and the 'thing,' whatever it is, that causes them--that is to say, we