study of science, because there is one more technical term to be learnt.

This difficulty is especially great in the science of political economy. We there deal with such familiar ideas as wealth, money, value, currency, capital, labour, exchange, but it is the very familiarity of the ideas which occasions. the greatest difficulty, because different people attach different meanings to the words, and infinite logomachy (Greek Móyos, word; páxn, battle), or disputes arising on merely verbal questions, is the result. Even if a writer carefully defines, the meaning in which he uses those terms he cannot oblige other persons to bear the definitions in mind. The other alternative of inventing wholly new terms is out of the question, as it would undoubtedly render a work intolerable to most readers. The only advice that can be given is to introduce a new term where it is likely to be readily accepted and to displace an old ambiguous term; but otherwise to endeavour to remove the ambiguity of the old term by constantly keeping in view a precise definition of the intended meaning.

A complete philosophical language will be composed of two distinct kinds of terms, which form respectively the descriptive terminology and the nomenclature of the science.

A descriptive terminology, as pointed out by Dr Whewell, must include all the terms required to describe exactly what has been observed concerning any object or phenomenon, in order that we may possess a permanent record of the observation. For every quality, shape, circumstance, degree or quantity there must be an appropriate name or mode of expression. Thus in recording the discovery of a new mineral we ought to be able to fix in words its exact crystalline form, its colour, its degree of hardness, its specific gravity, smell and taste if any,

and many other qualities which may possess importance. Modern botany arose from the efforts of Linnæus to create a system of terms by which every part and character of a plant can be accurately described. The language of botany, as since improved, presents the most complete instance of a scientific terminology. Geology suffers much, as I apprehend, from the difficulty of finding accurate terms; such names as trap, basalt, gneiss, granite, tuff, greenstone, trachyte, porphyry, lava, &c., are exceedingly vague and almost impossible to define, and at the same time to distinguish. Where a quality does not admit of degree or quantity it only requires a single name; otherwise we must find some mode of exact measurement and expression. The invention of any instrument for measuring a quality which has been before unmeasured is always an important step in science, and the construction of the thermometer by Fahrenheit and the pendulum clock by Huyghens were great eras in science.

On the other hand, each science requires a nomenclature or collection of names for the distinct objects or classes of objects treated in it. In mineralogy the names of separate minerals, such as hæmatite, topaz, amphibole, epidote, blende, polybasite, form the nomenclature; in chemistry we have all the names of the elements, together with a vast apparatus of names for organic and other compounds, such as ethyl, acetyl, cyanogen, napthalin, benzol, &c. In astronomy the names of the planets, satellites, nebulæ, constellations or individual stars, form a nomenclature of by no means a perfect or convenient kind; and geology has similarly a nomenclature necessarily of an incomplete character, in the names of the successive formations, silurian, devonian, carboniferous, permian, triassic, eocene, miocene, pliocene, post-pliocene, &c.

It is evident that a nomenclature must possess names

of various degrees of generality, including individual objects if they need separate record, infimæ species if such there be, with wider classes, up to the summa genera, or widest notions embraced in the science. In astronomy we deal chiefly with the names of individual objects, and there is as yet but little scope for classification. In such natural sciences as botany or zoology there is seldom or never any need of names for individuals, as an indefinite multitude of individuals generally resemble each other very closely in a great number of properties, so as to constitute what has been called a natural kind. Mr Mill uses this term to denote " one of those classes which are distinguished from all others, not by one or a few definite properties, but by an unknown multitude of them; the combination of properties on which the class is grounded being a mere index to an indefinite number of other distinctive attributes."

According to Mr Mill's language he seems to include in a nomenclature only the names of supposed species; for he says:-"A nomenclature may be defined, the collection of names of all kinds with which any branch of knowledge is conversant; or more properly, of all the lowest kinds, or infimæ species, those which may be subdivided indeed, but not into kinds, and which generally accord with what in natural history are termed simply species." But the fact is that naturalists have now abandoned the notion that the species is any definite form; many species are divided already into subspecies and varieties, or even varieties of varieties; and according to the principles of Darwin's theory the subdivision might go on indefinitely. It is surely most reasonable to regard the natural kingdoms of vegetables and animals as arranged in an indefinite series of classes and subclasses, and all the names attaching to any such classes belong to the nomenclature.

Again, Mr Mill does not include in the nomenclature such general names as denote conceptions artificially formed in the course of induction and investigation. Accordingly, besides a terminology suited for describing with precision the individual facts observed, there is a branch of language containing 66 a name for every common property of any importance or interest, which we detect by comparing those facts: including (as the concretes corresponding to those abstract terms) names for the classes which we artificially construct in virtue of those properties, or as many of them, at least, as we have frequent occasion to predicate any thing of." As examples of this class of names he mentions Circle, Limit, Momentum, Civilization, Delegation, Representation. While the nomenclature contains the names of natural classes, this third branch of language would apparently contain the names of artificial ideas or classes.

But I feel great difficulty in giving a clear account of Mr Mill's views on this subject, and, as my object in these Lessons does not allow of the discussion of unsettled questions, I must conclude by referring the reader who desires to continue the subject, to the 4th and 6th chapters of the 4th Book of Mr Mill's System of Logic, which treat of the Requisites of a Philosophical Language.

See Dr Whewell's "Aphorisms concerning the Language of Science," at the end of his Philosophy of the Inductive Sciences.

Thomson's Outline of the Laws of Thought, contains most interesting remarks on the general nature and use of Language, §§ 17—31.

QUESTIONS AND EXERCISES.

LESSON 1.-Introduction.

1. What are the meanings of a Law of Nature, and a Law of Thought?

2. Explain the distinction between the Form of Thought, and the Matter of Thought.

3. In what sense may Logic be called the Science of Sciences?

4. What is the derivation of the name Logic?

5. How does a Science differ from an Art, and why is Logic more in the form of a Science than an Art?

6. Can we say that Logic is a necessary aid in correct reasoning, when persons who have never studied logic reason correctly?

LESSON II.-Three Parts of Logic.

1. Name the parts of which a syllogism is composed. 2. How far is it correct to say that Logic is concerned with language?

3. What are the three acts of mind considered in Logic? Which of them is more especially the subject of the Science?

4. Can you state exactly what is meant by a generalnotion, idea, or conception?

5. How do the Nominalists, Realists, and Conceptualists differ in their opinions as to the nature

of a general notion?

6. What is the supposed fourth part of Logic?