Understandable sentences

Sentences that are long or complex are difficult for readers to process, especially if the grammar and structure are unfamiliar.

This section covers:

Sentence length

The average sentence length of your text is found by counting the number of words in sentences and dividing by the number of sentences. But, just as for average word length, this is only a rough measure of how difficult or easy the text will be to read.

The ideal average sentence length depends on the audience. In general, the broader the audience, the shorter the sentences should be: an average of 15 words per sentence for text for a general audience and no more than 25 words per sentence for more technical text. Your content is more likely to be understood by those with limited English if it is expressed in shorter sentences.

This does not mean that shorter is always better. Even very short sentences can be less readable if they chop the material up too much. A paragraph of 4 very short sentences may actually be less readable and convey less meaning than a paragraph of 2 longer sentences:

It was hard to sleep. I had a job interview. I was nervous. I really wanted the job.

It was hard to sleep because I was nervous. I had a job interview in the morning, and I really wanted the job.

A mix of shorter and longer sentences that are connected is the best way to keep readers engaged. Too many short sentences can lose meaning; too many long ones lose the connections between sentences in a haze of words. See Clear and appropriate language for further discussion of sentence lengths for different publications.

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Sentence order and complexity

Readers naturally find it easier to process sentences that present the subject matter in a meaningful order. For example, you would probably find the first example below easier to read than the second:

Longer sentences can make it difficult to understand the meaning, because they keep adding more words and more details before the reader reaches closure with the final full stop. [29 words]

Longer sentences that keep adding more words before the reader reaches the final full stop can be difficult to understand. [20 words]

Although the second sentence is shorter than the first, it may be more difficult for readers because its main idea (longer sentences are difficult to understand) is broken up by other words that are not as important. Readers have to detour through the less important words before coming back to the main statement to finish the sentence. In the longer version, the main idea is delivered in full at the start of the sentence, and other information is added after it.

Complex sentence construction can cause particular difficulty for readers of English as a second language, especially if the grammar and sentence order in the user’s first language are different from English.

For example, in English sentences, different sentence openings can be used to vary the focus, but their variability is a known challenge for second-language users:

The workers reported the accident with the stamping machine to the supervisor. He agreed to meet union representatives to discuss the problem. Until it was resolved, all production would be suspended.

The first 2 sentences in this example start with the same structure – the subject and an active verb. But the third sentence starts with a conditional clause, and is also more passive. This variation is fine for first-language users of English, and probably helps to refresh their attention. But for second-language users, it may make it difficult to understand the continuity between the 3 sentences.

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