We can gain some idea of this necessity of things for thought by examination of the structure of a proposition.
Let us suppose that a proposition is being communicated by an expositor to a recipient.

Such a proposition is composed of phrases; some of these phrases may be demonstrative and others may be descriptive.
By a demonstrative phrase I mean a phrase which makes the recipient aware of an entity in a way which is independent of the particular demonstrative phrase.

You will understand that I am here using 'demonstration' in the non-logical sense, namely in the sense in which a lecturer demonstrates by the aid of a frog and a microscope the circulation of the blood for an elementary class of medical students.

I will call such demonstration 'speculative' demonstration, remembering Hamlet's use of the word 'speculation' when he says, There is no speculation in those eyes.
Thus a demonstrative phrase demonstrates an entity speculatively.

It may happen that the expositor has meant some other entity--namely, the phrase demonstrates to him an entity which is diverse from the entity which it demonstrates to the recipient.