A Sentence Is a Unit of Attention

B · Plate 06 in the Plain Language series · Other Communications

Advice about sentence length is usually given as a number, and the number is usually wrong. Prose made entirely of short sentences is exhausting in a different way from prose made of long ones. The useful measure is not words but open commitments: how many things the reader is holding unresolved at any moment.

A sentence that begins with a subordinate clause asks the reader to keep it suspended until the main clause arrives. One suspension is comfortable and often elegant. Two nested inside each other are a cost. Three are a wall, and readers do not climb walls in material they did not seek out; they leave.

Where the load falls

The load is heaviest at the start of a sentence and lightest at the end. Material placed before the main verb has to be carried; material placed after it can be absorbed as it arrives. This is why a long sentence that front-loads its qualifications feels much longer than a sentence of the same length that states its point and then extends.

The practical form of this is to put the subject and verb close together and early, and to let the sentence grow to the right. Such sentences can be long without being difficult, because the reader has somewhere to attach each new piece as it comes. The comparison is with a shelf: the shelf has to exist before anything can be put on it.

Rhythm as a signal

Variation in length is not decoration. It tells the reader where the emphasis lies. A short sentence after several long ones lands hard, which is why the short sentence should carry the thing worth landing. A short sentence carrying a trivial point wastes the loudest instrument in the paragraph, and the paragraph after it has to work harder to be heard.

The corollary is that emphasis cannot be added later with typography. Bold text, italics and capitals are asking the design to do what the sentence structure failed to do. They also lose their force by repetition much faster than rhythm does: the third bold phrase on a page is read as ordinary text, while the third short sentence still lands.

Paragraphs and the same logic

A paragraph obeys the same rule at a larger scale. Its first sentence sets a commitment and its last resolves one. A paragraph that opens by naming its subject and closes by completing the thought can be long. A paragraph that opens with context and never quite reaches its point is hard to read at any length, and is the usual cause of the complaint that a text is dense.

The revision that helps most is also the crudest: find the sentence in each paragraph that says what the paragraph is for, and move it to the front. Some paragraphs turn out not to contain one, and those are the paragraphs to rewrite or cut. The exercise is mechanical enough to do on a tired afternoon, which is a real advantage in a discipline where most advice requires being at one's sharpest.

None of this argues for simplicity as a virtue in itself. Complicated subjects need complicated sentences, and flattening them produces a text that is easy to read and impossible to act on. What the reader cannot afford is complication that is accidental: a clause suspended because of the order in which the writer happened to think of things, rather than because the thought required it.