Ideas are the smallest units of thought that can be communicated. Ideas may run to many words in expression because they require a structure of words to reproduce their context. Word are required to transmit to one context a thought that is wordlessly implicit in another, an idea, which may be a limitlessly subtle inflection of its original context. At the right time, a few gestures, indeterminate in themselves, totally dependent for their meaning, may express all that a sentence can tell at the wrong time. (I indulge in the parable of an ancestor who on the hunt, by no more than the slightest stirring of the arm and extension of the finger, indicated, "No, the other way," and turned failure into success.)
The constituents of the minimum unit of communicable thought must be units of incommunicable thought. I name these evocations, since they are recognized as evocative. The mind cannot make its own evocations; it must collect them as surely as a bird must collect grit for its gizzard. And like a gizzard stone a single evocation may remain in use for a long time, with a valency that internally and unconsciously parallels the external and conscious use of a tool.
Being incommunicable, evocations cannot be defined. Yet they can be traced. What is it that the mind seeks out, hoards, counts over? What mental experiences, without uses of their own, are approached with the same gravity as the most useful tasks? Review the mind's senses: how an image burns onto the mind's eye; how a word echoes and echoes in the mind's ear.
Victims of trauma are at the mercy of recurrence and flashback—at the mercy of the little things, the little fragments of experience, the mere reminders that reel them backwards into memory. This is a warped mirror and retrogradation of a healthy movement of the mind. Reminders drag backwards into memory; evocations lead forward to ideas.
Though evocations are usually single words or images, they need not be. Some evocations are ideas in themselves, constituent to more complex ideas. Whole works of art, whole journeys, whole friendships may be valent as evocations. In certain moods the whole world seems to me the evocation of some superb and singular idea I would lose my soul to enphrase—like an utterer of God's true name, a seraph would circle me to either side, declaring that I had gained the world, and lost the world to come.
A simple example of the use of evocations is at hand. A word catches the attention of a reader. The word is obscure, a little grandiloquent, but it charms him. It has a good rattling rhythm to it, almost a swing. A single stop between two liquids to one side, and a liquid and a sibilant to the other anticipate a euphonious final consonant cluster. Moreover it has a valency that he cannot quite define. Some time later this reader becomes conscious of blogs and the interesting things being done with them. Surely this is an opportunity; but what can he do? He lacks the quickness and lightness for blogging as such. Too often has nothing to say. So he puts the thought aside until he reads Boswell tell how Johnson wrote out a number of the Rambler with the printer's devil looking on. Then he has an idea: "Of course—not ruricolist—The Ruricolist!"