Two great disputes connect themselves with percep- tion, both raised into their full prominence in the phil- osophical world by bishop Berkeley. The first is the origin of our judgments of the distances and real mag- nitudes of visible bodies. In opposition to the com- mon opinion on this subject, Berkeley maintained that these were learned by experience, and not known by the mere act of vision. The second question relates to the grounds we have for asserting the existence of an external and material world, which, in the view of Berkeley, was bound up with the other. Inasmuch as perception is a mental act, and knowledge is something contained in a mind, what reason have we for believ- ing in the existence of objects apart from our minds .' or what is the mode of existence of the so-called ex- i ternal world ? The following sentences show in what j manner Berkeley opened up the question : " That nei- ther our thoughts nor passions nor ideas, formed by the imagination, exist without the mind, is what ev- erybody will allow ; and it seems no less evident that , the various sensations or ideas imprinted on the sense, ! however blended or combined together (i. e. whatever : objects they compose), cannot exist otherwise than in ' a mind perceiving them. I think an intuitive knowl- edge may be obtained of this by any one that shall at- tend to what is meant by the term exist when applied to sensible things. The talile I write on I say exists ! — i. e. I see and feel it ; and if I were out of m}' study, 1 I should say it existed, meaning thereb}- that if I was ■ in my study I might perceive it, or that some other spirit actually does perceive it. There was an odor — i. e. it was smelled ; there was a sound — that is to say, it was heard ; a color or figure, and it was perceived by sight or touch. This is all I can understand by these and the like expressions. For as to what is said of the absolute existence of unthinking things, without any relation to their being perceived, that seems per- fectly unintelligible. Their esse is percipi, nor is it possible they should have any existence out of the minds or thinking things which perceive them." See Berkeley. This doctrine of Berkeley, amounting, it was said, to <a denial of the existence of a material world (which is far from a correct view of it), was fol- lowed up by Hume, who, on similar reasoning, denied the existence of mind, and resolved the universe into a mere flow of ideas and impressions without any sub- ject to be impressed, acknowledging, nevertheless, that he felt himself unable, practically, to acquiesce in his own unanswerable arguments. There was obvi- ously some great mistake in a mode of reasoning that brought about a dead-lock of this description ; and hence it has been the work of metajihysical philosophy since that time to endeavor to put the perception of the world on an admissible footing. Dr. Ileid re- claimed against Berkeley and Hume by appealing to common-sense, or unreasoning instinct, as a sufficient foundation for our belief in the existence of a world apart from our own minds. Sir "William Hamilton has expounded the same view with greater clearness and precision. He considers that our consciousness tells us at once that in the act of perceiving there is both a. perceivitig subject — self, or the mind — and an ex- ternal reality, in relation with sense, as the object per-
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ceived. " Of the existence of both these things," he j savs, " I am convinced ; l)ecause I am conscious of knowing each of them, not mediately in something j else, as represeiiied, but immediately in itself, as exist- ing. Of their mutual dependence I am no less con- vinced, because each is apprehended equally and at once, in the same indivisible energy, the one not pre- [ ceding or determining, the other not following or de- ' terniined ; and because each is apprehended out of and in direct contrast to the other" (M ori\s, p. 747). Much as Hamilton has labored to elucidate this doc- trine in all its bearings, it has not been universally accepted as satisfactory. Manj' believe that he has regarded as an ultimate fact of our constitution what admits of being still further resolved, and has mis- taken an acquisition of the mature mind for a prim- itive or instinctive revelation. Professor Ferrier, in liis Institutes of Metaphysics, has gone throu;^h the question with extraordinary minuteness and elabora- tion. His main position is the inseparability of the subject and the object in perception (a position also maintained by Hamilton in the above extract), which is not reconcilable with the common assumption as to the independent existence of matter. Indeed, he re- duces the received dogma of the existence of matter per se to a self-contradiction, and builds up a sj'stem in strict conformitj' -with the correlation, or necessary connection, of the mind perceiving with the object per- ceived. Hs thus approaches nearer to Berkeley than to Hamilton or to Keid. — Chambers. See Porter, In- tellect ; Ueberweg, Hist, of Philos. ; South. E v. Oct. 1873, art. viii ; ]Vest7n. Rev. Jan. 1873, p. 119.