By a noun we mean a sound significant by convention, which has no reference to time, and of which no part is significant apart from the rest. In the noun ‘Fairsteed,’ the part ‘steed’ has no significance in and by itself, as in the phrase ‘fair steed.’ Yet there is a difference between simple and composite nouns; for in the former the part is in no way significant, in the latter it contributes to the meaning of the whole, although it has not an independent meaning. Thus in the word ‘pirate-boat’ the word ‘boat’ has no meaning except as part of the whole word.

The limitation ‘by convention’ was introduced because nothing is by nature a noun or name-it is only so when it becomes a symbol; inarticulate sounds, such as those which brutes produce, are significant, yet none of these constitutes a noun.

The expression ‘not-man’ is not a noun. There is indeed no recognized term by which we may denote such an expression, for it is not a sentence or a denial. Let it then be called an indefinite noun.

The expressions ‘of Philo’, ‘to Philo’, and so on, constitute not nouns, but cases of a noun. The definition of these cases of a noun is in other respects the same as that of the noun proper, but, when coupled with ‘is’, ‘was’, or will be’, they do not, as they are, form a proposition either true or false, and this the noun proper always does, under these conditions. Take the words ‘of Philo is’ or ‘of or ‘of Philo is not’; these words do not, as they stand, form either a true or a false proposition.