There are two uses of examples or images--in the first place, they suggest thoughts--secondly, they give them a distinct form. In the infancy of philosophy, as in childhood, the language of pictures is natural to man: truth in the abstract is hardly won, and only by use familiarized to the mind. Examples are akin to analogies, and have a reflex influence on thought; they people the vacant mind, and may often originate new directions of enquiry. Plato seems to be conscious of the suggestiveness of imagery; the general analogy of the arts is constantly employed by him as well as the comparison of particular arts--weaving, the refining of gold, the learning to read, music, statuary, painting, medicine, the art of the pilot--all of which occur in this dialogue alone: though he is also aware that 'comparisons are slippery things,' and may often give a false clearness to ideas. We shall find, in the Philebus, a division of sciences into practical and speculative, and into more or less speculative: here we have the idea of master-arts, or sciences which control inferior ones. Besides the supreme science of dialectic, 'which will forget us, if we forget her,' another master-science for the first time appears in view--the science of government, which fixes the limits of all the rest. This conception of the political or royal science as, from another point of view, the science of sciences, which holds sway over the rest, is not originally found in Aristotle, but in Plato. The doctrine that virtue and art are in a mean, which is familiarized to us by the study of the Nicomachean Ethics, is also first distinctly asserted in the Statesman of Plato. The too much and the too little are in restless motion: they must be fixed by a mean, which is also a standard external to them. The art of measuring or finding a mean between excess and defect, like the principle of division in the Phaedrus, receives a particular application to the art of discourse. The excessive length of a discourse may be blamed; but who can say what is excess, unless he is furnished with a measure or standard? Measure is the life of the arts, and may some day be discovered to be the single ultimate principle in which all the sciences are contained. Other forms of thought may be noted--the distinction between causal and co-operative arts, which may be compared with the distinction between primary and co-operative causes in the Timaeus; or between cause and condition in the Phaedo; the passing mention of economical science; the opposition of rest and motion, which is found in all nature; the general conception of two great arts of composition and division, in which are contained weaving, politics, dialectic; and in connexion with the conception of a mean, the two arts of measuring.