We can define the names of minerals, for example, in terms of chemistry and mineralogy, as when we say that the ordinary meaning of the English word ‘salt’ is ‘sodium chloride (NaCl)’, and we can define the names of plants or animals by means of the technical terms of botany or zoology, but we have no precise way of defining words like ‘love’ or ‘hate’, which concern situations which have not been accurately classified — and these latter are in the great majority. ([2], p. 139.)