To clearly convey an idea in the writer’s mind, a sentence should only be as long as it needs to be. It could be as short as two or three words, as “That’s all” in the old Nat King Cole song or “Call me Ishmael” in the opening line of Herman Melville’s
Moby Dick. On the other hand, the sentence could be all of 4,391 words, which is how long
Molly Bloom’s soliloquy is in James Joyce’s novel
Ulysses; this indomitable wordage, however, pales in comparison with a 13,955-word sentence in British novelist Jonathan Coe’s
The Rotter’s Club, which Wikipedia says “appears to hold the record for the Longest English sentence in English literature.” (This time I won't bother you with a link to a quote.)
My point in citing these highly disparate sentence lengths in published English works is that there really isn’t any rule as to how long a sentence should be. It all depends on how simple or complex the mind of the writer runs, on the personal writing style that he or she has developed, and on the kind of audience being addressed. For practical purposes as opposed to literary purposes, however, I would recommend brevity in sentence construction all the time in the interest of clarity. In particular, I do think that a newspaper reporter would be making a hateful imposition on the reader by habitually writing news-story sentences far in excess of, say, 20-25 words; that a TV news writer would cause confusion and consternation among both news readers and TV audiences by foisting 30-word sentences on them even just occasionally; and that a speaker on the lecture circuit would make audiences doze off without fail by droning on and on with sentences way beyond 30-40 words.
Admittedly, though, the preceding 85-word sentence above would seem to contradict my very own prescriptions for sentence length. Well, it does, but I suggest that we look at this contradiction as another important aspect of sentence word-counts. Punctuation does change the sentence-length paradigm altogether. Indeed, the judicious use of punctuation marks—the comma, semicolon, colon, dash, ellipsis, and parenthesis—makes it possible for us to write high word-count, many-idea sentences without overwhelming our readers or listeners. This, however, is another aspect of sentence construction that we should look at more closely some other time.
