A sentence gets hard when the reader has to hold a subject in mind while something long passes between it and its verb. The report, which was commissioned last year by a committee that no longer exists, says: by the time says arrives, the reader has been carrying the report for fifteen words with nothing to do with it.
Length is what people notice and distance is what causes the trouble. A thirty-word sentence whose subject and verb sit together is easy; a sixteen-word sentence with eleven words wedged in the middle is not.
Eight rules that fix most sentence problems
- a sentence needs a subject and a verb, and a group of words without both is a fragment however long it is.
- a fragment has no main verb. Which was the reason for the delay is not a sentence, and this is the commonest error in careful writing.
- comma splices join with a comma and should not. It rained, the match was cancelled needs a full stop, a semicolon or a joining word.
- and, but, so join two sentences with a comma before them, which is the ordinary repair for the error above.
- however takes a semicolon or a full stop, never a comma on its own, because it is an adverb rather than a conjunction.
- which takes a comma and that does not, and the difference changes whether the clause identifies or merely adds.
- the passive hides the doer, which is sometimes exactly right and is usually worth noticing before you commit to it.
- start with the subject unless you have a reason. English puts old information first and new information last, and moving things about breaks that.
Where a sentence can be cut
English lets you break wherever a complete clause ends, and the practical version of that rule is short: find the conjunction and replace it with a full stop: and, but, so, because, which, although. Most over-long sentences in second-language English are two or three perfectly good sentences that were joined at one of those words.
The joining is rarely a decision. It happens because a sentence that is still running feels unfinished, and a writer who is not sure the point has landed keeps adding rather than stopping. The result is a tail: a clause hanging off a clause hanging off a clause, each one added to clarify the one before it.
Cutting a tail is not a stylistic preference. Each break lets the reader put something down, and a reader who has been allowed to put four things down has capacity for the fifth.
Where it stops: the relative clause chain
The stall is building by extension, and it is the commonest shape in competent second-language prose. A writer produces a sentence, wants to qualify it, and adds which. Then the qualification needs its own qualification, and adds that. Nothing in the process is wrong, every clause is correct, and the sentence has grown a tail three joints long.
What makes it a stall rather than an error is that no tool flags it and no reader complains in a way that names it. The feedback that arrives is that the writing is dense, or formal, or hard work, and none of those words points at the mechanism, so the writer tries to simplify the vocabulary instead and the sentences stay exactly as they were.
The habit is worth attacking directly, because the fix is mechanical. Take any sentence with two relative clauses in it and rewrite it as two sentences. Do that for a page and the page changes character.
Rhythm is a length that varies
Once the sentences are cut, the danger is uniformity. A page of short sentences is as tiring as a page of long ones and for the same reason: a reader who can predict the shape of the next sentence stops reading it attentively.
The usable rule is that a long sentence should be earning its length by carrying a real qualification, and that it should be surrounded by short ones. One long sentence among short ones is emphasis. Four in a row is a texture, and a texture is what a reader skims.
Somebody else's before and after
The Plain English Campaign publishes its guides free, and what makes them useful here is not the advice but the rewrites: a real sentence from a real document, followed by the same content in half the words, with nothing important lost. Reading twenty of those does more for a writer than any rule, because the rule is abstract and the pair is specific.
They replaced a house style manual that existed on paper inside one organisation and was seen by nobody outside it. The limitation is the register they aim at: this is public-information writing, plain and short by design, and an academic argument or a literary paragraph needs sentence shapes their guides would flag. Take the cutting, and do not take the ceiling.
What it looks like when it goes wrong
The recognisable failure is a sentence whose main verb arrives so late that the reader has to go back to find the subject. If a reader has to re-read a sentence of yours to parse it rather than to think about it, the fault is nearly always distance.
The second failure is the comma splice arriving as a repair. A writer who has been told to shorten sentences cuts one and joins the halves with a comma, which produces two sentences glued at a punctuation mark that cannot hold them, and that is a mechanical error rather than a stylistic one: commas, semicolons and apostrophes, settled.
What the sentences are supposed to add up to, and why a correct one can still fail to connect to the one before it, is one idea, an opening line, and how the next one connects, and the rules that decide where a break is legal at all are who, which and that, and where the comma goes.
The open question is where the sentence shapes come from in the first place. Nobody writes a shape they have never read, so a writer whose English arrives entirely through a course will produce a course's sentences: getting through more of it without losing the meaning.