Words are needed when we have to attend to the general plan of any system, as in thinking about organisms with reference to their type, or about political relations--about anything, that is, which is not of such a nature that the members of the idea can be symbolised in pictorial form. It would be difficult, for example, to comprehend the respiration of plants under a symbolic picture-idea drawn {81} from the respiration of the higher animals. The relations which constitute a common element between the two processes do not include the movements, feelings, and visible changes in the circulatory fluid from which our image of animal respiration is chiefly drawn; and we could hardly frame a pictorial idea that would duly insist on the chemical and organic conditions on which the common element of the process depends. In a case of this kind the word is the symbol which enables us to hold together in a coherent system, though not in a single image, the relations which make up the content of our thought. “Words” may be of many different kinds--spoken, written, indicated by deaf and dumb signs; all of these are derived from the word as it is in speech, although writing and printing become practically independent of sound, and we read, like the deaf and dumb alphabet, directly by the eye. Then there may be any kind of conventional signals either for letters, words, or sentences, and any kind of cipher or _memoria technica_ either for private or for general use--in these the “conventional” nature of language reaches its climax, and the relation to a natural growth of speech has disappeared. And finally there are all forms of picture-writing, which need not, so far as its intrinsic nature goes, have any connection with speech at all, and which seems to form a direct transition between picture-thinking and thinking through the written sign. All these must be considered under the head of language, as a fixed system or signs for meanings, before we can ultimately pronounce that we think without words. Every Judgment, however, can be expressed in words, {82} though not every Judgment need be so expressed or can readily be so. _Proposition and sentence._ 2. A Judgment expressed in words is a Proposition, which is one kind of sentence. A command question or wish is a sentence but not a proposition. A detached relative clause [1] is not even a complete sentence. The meaning of the imperative and the question seems to include some act of _will_; the meaning of a proposition is always given out simply for fact or truth. We need not consider any sentence that has no meaning at all. [1] See above, Lect. IV. _Difference between Proposition and Judgment_ 3. Almost all English logicians speak of the Proposition and not of the Judgment. [1] This does not matter, so long as we are agreed about what they mean. They must mean the proposition _as understood_, and this is what we call the judgment. [1] So Mill, Venn, Jevons, Bain (see his note, p. 80).