There has been so much confusion of thought generated by the mere word-jugglery of philosophers in the use of the terms _time_ and _space_, _duration_ and _extension_, _eternity_ and _immensity_, that a revision of the whole terminology in the interest of true science is demanded. It is perilous to launch out upon this ocean of equivocal phraseology, called the philosophy of time and space, before taking our bearings, amid notions so closely related, yet so dissimilar, and endeavoring to fix some definite meaning to these terms, which, like points of the compass, shall enable us to find our position. 1. _Let us commence our effort with_ SPACE, EXTENSION, _and_ IMMENSITY. Some philosophers--Cousin,[77] Hamilton,[78] Spencer,[79] McCosh,[80] for example--confound _space_ and _extension_, and all of them confound both with absolute _immensity_.[81] Now if space is identical with extension, it must be cognized by the senses and the sensuous imagination. This is unhesitatingly affirmed by Hamilton: "We _see_ extension," and "by the name extension we designate our empirical knowledge of space."[82] So also McCosh: "Of space in the concrete we have an immediate knowledge by the senses, certainly by some of them, such as the touch and sight."[83] Space in this connection can not therefore be regarded as an _à priori_ cognition. It is equally obvious that if space is identical with extension, it must have color and form. This also is admitted by Hamilton: "I can easily annihilate all corporeal existence [in imagination]. I can imagine _empty_ space. But there are two attributes of which I can not divest it--that is, shape and color."[84] Now if space has "shape," that is, figure, it must have dimensions, and accordingly we find almost all philosophers speaking of the three dimensions of space--length, breadth, and depth. That which has length, breadth, and depth must be divisible, must have parts and proportions, must have susceptibilities of exact measurement, and therefore must be _finite_. This again is the doctrine of Hamilton: "Space is finite, and a finite, that is, a bounded space constitutes a figure"--a sphere.[85] The fundamental doctrine of Hamilton is that "space, like time, is only the intuition or the concept of a certain correlation of existence--of existence, therefore, _pro tanto_, _as conditioned_. _It is thus itself only a form of the conditioned._"[86] But if space be only a correlation of conditioned, and therefore finite existence, how can he speak of it "being conceived as infinite,"[87] and, above all, how can he speak of "the absolute totality" and "the infinite immensity of space."