Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that he make every word tell. – Strunk and White, The Elements of Style
Common wisdom holds that that, both generally and in scientific writing, shorter sentences are always better. Furthermore, it is often assumed that second-language English speakers must pay special attention to sentence length due to a tendency toward wordiness. As a result, many second-language English speakers writing scientific manuscripts are concerned about shortening their sentences during the revision process.
However, scientific manuscripts are known for their long sentences. One set of guidelines for authors (from Elsevier) claims that the average sentence length in scientific manuscripts is 12-17 words, whereas another source reports an average of 25-30 words in the peer-reviewed literature, with some sentences running at over 60 words in the sample studied. For comparison, the average sentence length for Harry Potter author JK Rowling, who can be considered representative of a modern English writer with a general audience, is 12 words, and the first half of this sentence contains 26 words. Many manuscript preparation resources advise researchers to shorten their sentences to approximately 20 words to ensure readability.
Interestingly, in articles submitted or accepted for publication, sentences written by authors for whom English is not their first language may actually be shorter than those written by their English-speaking counterparts. A study conducted on articles in the British Journal of Surgery found that the sentences and words (measured in syllables) used by second-language speakers were statistically significantly shorter than those used by first-language English speakers. This can be attributed to the tendency of first-language speakers to use longer, more complex sentence constructions. Furthermore, with less pressure to focus on writing quality, first-language speakers may be less diligent about avoiding wordiness.
Rather than attempting to tailor each sentence to fit a prescribed word length, consider focusing on the amount of information conveyed per sentence instead. A sentence is too long if, upon reaching the end, your reader cannot remember how the sentence began. Writers are often advised to make sure that each sentence conveys only one idea; however, it can be difficult to decide what delimits “one idea,” especially when reporting results. An alternative approach is to think of the breaks between sentences as “understanding checkpoints” for your reader—places in the narrative where the reader should pause and parse the information presented before continuing.
It is also important to note that an average sentence length is just that — an average. Even writers who opt to aim for an average sentence length of, e.g., 20 to 25 words should mix long and short sentences to keep their reader’s interest. Long sentences work best when your reader’s interest is piqued, as these sentences have the advantage of flow but require more focus on the part of the reader. Meanwhile, short sentences grab your reader’s attention. These sentences are ideal for keeping your reader engaged, but too many consecutive short sentences are jarring. Mixing these two sentence types keeps your audience engaged throughout the paragraph.
In sum, “shorter is better” is an oversimplification for sentence length in scientific manuscripts. Instead, both first-language and second-language English speakers should ensure that each sentence is an appropriate length for the idea it expresses.
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