The idea, or the nature of the combination intended to be expressed by the speaker, need not be completely represented by words in order to render fully intelligible the thought present in the mind of the speaker. Much less than a complete expression will often suffice.

If a sentence is the means of inducing a certain combination of at least two ideas in a hearer’s mind, a complete sentence must necessarily consist of at least two parts. We shall later discuss those sentences in which only one of the two parts is expressed in words, and shall here confine our attention to the complete sentence. Grammar teaches us that a complete sentence consists of a subject and a predicate. Now, these grammatical categories are undoubtedly based upon a psychological distinction; but we shall soon see that it does not necessarily follow that the grammatical and psychological subject, or the grammatical and psychological predicate are always identical. The PSYCHOLOGICAL SUBJECT expresses the conception which the speaker wishes to bring into the mind of the hearer; the PSYCHOLOGICAL PREDICATE indicates that which he wishes him to think about it. This, and no more than this, is required to impart to any collection of words the nature of a sentence.

In grammar we commonly attach a much more restricted meaning to the terms ‘subject,’ ‘predicate,’ and ‘sentence.’ For instance, when the predicate is a noun, we demand that the normal sentence should express the comprehension of the subject in a wider class; as, John is a boy: or that it should express some quality of the subject; as, John is good: or, lastly, that the subject be identical with the predicate; as, John is King of England. But in reality we have, in many sentences, noun-predicates which show us relations of quite another kind, expressed by the mere collocation of subject and predicate, as in many proverbs and proverbial expressions; e.g., One man, one vote; Much cry and little wool; First come, first served; A word to the wise; Like master, like man; Better aught than naught; Small pains, small gains. This is the way in which children make themselves intelligible; as, Papa hat, for Papa has a hat on: and this is the way in which even adults endeavour to express their meaning to foreigners when the latter have not mastered more of the language than perhaps a few nouns, viz. by mentioning the objects which they wish to bring under the notice of their companions, and trusting to the situation to enable these to understand their meaning. We say, Window open, and we are understood by the foreigner to mean that the window is open, or that we wish it open, as the circumstances may show.

Originally, there was only one method of marking the difference between subject and predicate, viz. stress of tone; as, e.g., in the instance which we just gave, of ‘Window open.’ If these words are pronounced with a great stress on ‘window,’ we at once perceive them to mean, The thing which is (or which I wish to be) open is the window. If, on the other hand, we exclaim, ‘Window OPEN,’ with stress on ‘open,’ we at once convey the sense, The window is (or must be) open, not closed. This shows that, in the case of such isolated instances, the psychological predicate has the stronger accent, as being the more important part of the sentence, and the part containing the new matter. Again, the place held in the sentence by the subject and predicate respectively, may have afforded another means of distinction between the two. Different views have been held as to the respective precedence of subject and predicate in the consciousness of the speaker. The true view seems to be that the idea of the subject is the first to arise in the consciousness of the speaker; but as soon as he begins to speak, the idea of the predicate, on which he wishes to lay stress, may present itself with such force as to gain priority of expression, the subject not being added till afterwards. Take, for example, the opening of Keats’ Hyperion— ‘Deep in the shady sadness of a vale
Far sunken from the healthy breath of morn,
Far from the fiery noon, and eve’s one star,
Sat grey-haired Saturn, quiet as a stone.’
In this case, the superior emphasis gained by the position of the predicate in the first place causes the speaker to set it there, and is indicative of the superior importance which he attaches to it.[29]

Similarly, the subject is sometimes expressed first by a pronoun, whose relation only becomes clear to the listener when expressed more definitely at a later period; as— ‘She is coming, my dove, my dear.’
(Tennyson, Maud.)
‘She dwelt among the untrodden ways
Beside the springs of Dove,
A maid whom there were none to praise
And very few to love.’
(Wordsworth, The Lost Love.)
‘She was a staid little woman, was Grace.’
(Dickens, Battle of Life.)
This construction is extremely common in French; as, ‘Elle approche, cette mort inexorable;’ ‘Mais ce qu’elle ne disait point, cette pauvre bergère.’

The transposition, then, of subject and predicate may be considered an anomaly; but it is an anomaly of frequent occurrence, and is based on the importance which the predicate assumes in the mind of the speaker.

We have seen that single words may possess concrete and abstract significations,[30] and it is the same with sentences. A sentence is concrete when either the psychological subject or the psychological predicate is concrete; as, This man is good. But as far as the mere form goes, concrete and abstract sentences need not differ; for instance, an expression like The horse is swift (which, when it does not refer to any particular horse, is an ‘abstract’ sentence) is identical in form with the expression The horse is worthless, which obviously refers to some particular horse, and is therefore ‘concrete.’ It is the situation and circumstances alone which mark the different nature of the sentences. There are, however, sentences which, with a concrete subject, have a partially abstract meaning. If, for instance, on hearing a lady sing, one remarks, She sings too slowly, the sentence is entirely concrete; but the same words may be used to express that the singer is in the habit of singing too slowly, in which case the predicate becomes abstract. Such sentences may be called ‘concrete abstract.’

It was stated that at least two members are necessary to make up a sentence. It seems, at first sight, a contradiction to this statement that we find sentences composed of merely a single word, or of a group of words forming a unit. The fact is that, in this case, one member of the sentence is assumed and finds no expression in language. Commonly this member is the logical subject. This subject may, however, be completed from what precedes, or is sufficiently clearly indicated by the circumstances of the case; or, again, in conversation, it is often necessary to take it from the words of the other speaker. The answer is frequently a predicate alone; the subject may be contained in the question, or the whole question may be the logical subject. If I say, Who struck you? and the answer is John, the subject is, in this case, contained in the question, and the answer is, ‘The striker is John.’ If I say, Was it you? the whole question is the logical subject, and the answer, Yes, No, Certainly, Surely, Of course, etc., is the logical predicate, as if the reply had been, ‘My being so is the case.’ Many other similar words may serve as the predicate to a sentence spoken by another, such as Admittedly, All right, Very possibly, Strange enough, No wonder, Nonsense, Stuff, Balderdash, etc.

In other cases, the surrounding circumstances, or what is called ‘the situation,’ forms the logical subject. If I say, ‘Welcome!’ and at the same time stretch out my hand to a new arrival, this is equivalent to saying, You are welcome, and welcome is the logical predicate. In exclamations of sudden astonishment and alarm, such as Fire! Thieves! Murder! Help! it is the situation which is the logical subject. Challenges are instances of the same kind, e.g. Straight on or not? Right or left? Back or forward? When the poet sings— ‘A wet sheet and a flowing sea,
A wind that follows fast,
And fills the white and rustling sail,
And bends the gallant mast,’
the situation, again, is the logical subject.

It should be noticed that, in the case of sentences expressed by a single member, the word which for the speaker is the psychological predicate becomes for the hearer the subject. A man, seeing a house on fire, cries ‘Fire!’ for him the situation is the subject, and the idea of fire is the predicate. The man who hears ‘Fire!’ cried before he himself sees it, conceives of fire as the subject, and of the situation as the predicate. Sentences may, however, occur in which both speaker and hearer apprehend what is uttered as the subject, and the situation as the predicate. Supposing, for instance, that two persons have agreed that the fire shall be extinguished before they go out, and one of them, observing the chimney smoking, cries out, ‘The fire!’ in this case the fire, the logical subject, is alone denoted, and the predicate is gathered by the person addressed from the situation, which is evident from the speaker’s gestures. If, again, two friends are travelling, and one remarks that the other is without his umbrella, the mere exclamation, ‘Your umbrella!’ suffices to make the latter complete the predicate. The vocative, again, pronounced as such, and intended to warn or entreat, suggests a psychological predicate which it lacks in words. On the other hand, by the side of a verb in the second person without subject pronoun, the vocative may be apprehended as the subject to the verb. If I say, ‘Come!’ the vocative (the person addressed) may be apprehended as the subject to this verb; if it be Charles, the meaning is, Charles should come.