This second kind of displacement occurring in dream-formation is not only of great theoretical interest, but also peculiarly well- fitted to explain the appearance of phantastic absurdity in which dreams disguise themselves. Displacement usually occurs in such a way that a colourless and abstract expression of the dream- thought is exchanged for one that is pictorial and concrete. The advantage, and along with it the purpose, of this substitution is obvious. Whatever is pictorial is capable of representation in dreams and can be fitted into a situation in which abstract expression would confront the dream-representation with difficulties not unlike those which would arise if a political leading article had to be represented in an illustrated journal. Not only the possibility of representation, but also the interests of condensation and of the censorship, may be furthered by this exchange. Once the abstractly expressed and unserviceable dream-thought is translated into pictorial language, those contacts and identities between this new expression and the rest of the dream-material which are required by the dream-work, and which it contrives whenever they are not available, are more readily provided, since in every language concrete terms, owing to their evolution, are richer in associations than are abstract terms. It may be imagined that a good part of the intermediate work in dream-formation, which seeks to reduce the separate dream- thoughts to the tersest and most unified expression in the dream, is effected in this manner, by fitting paraphrases of the various thoughts. The one thought whose mode of expression has perhaps been determined by other factors will therewith exert a distributive and selective influence on the expressions available for the others, and it may even do this from the very start, just as it would in the creative activity of a poet. When a poem is to be written in rhymed couplets, the second rhyming line is bound by two conditions: it must express the meaning allotted to it, and its expression must permit of a rhyme with the first line. The best poems are, of course, those in which one does not detect the effort to find a rhyme, and in which both thoughts have as a matter of course, by mutual induction, selected the verbal expression which, with a little subsequent adjustment, will permit of the rhyme.

In some cases the change of expression serves the purposes of dream-condensation more directly, in that it provides an arrangement of words which, being ambiguous, permits of the expression of more than one of the dream-thoughts. The whole range of verbal wit is thus made to serve the purpose of the dream-work. The part played by words in dream-formation ought not to surprise us. A word, as the point of junction of a number of ideas, possesses, as it were, a predestined ambiguity, and the neuroses (obsessions, phobias) take advantage of the opportunities for condensation and disguise afforded by words quite as eagerly as do dreams. * That dream-distortion also profits by this displacement of expression may be readily demonstrated. It is indeed confusing if one ambiguous word is substituted for two with single meanings, and the replacement of sober, everyday language by a plastic mode of expression baffles our understanding, especially since a dream never tells us whether the elements presented by it are to be interpreted literally or metaphorically, whether they refer to the dream- material directly, or only by means of interpolated expressions. Generally speaking, in the interpretation of any element of a dream it is doubtful whether it

(a) is to be accepted in the negative or the positive sense (contrast relation);

(b) is to be interpreted historically (as a memory);

(c) is symbolic; or whether