Sentence boundaries

A clause opening with because, although, while, since, if, when, after, unless, whereas cannot stand alone, however long it is. Attach it to the main clause with a comma when it comes first, and with nothing at all when it comes second: The committee postponed the vote because the report was late.

A participle is not a verb. The members meeting has a subject and something that looks like a predicate, which is exactly why the error survives proofreading. Ask what the subject actually does: if the only candidate ends in -ing with no is, was or were in front of it, the sentence has no verb.

A clause beginning which, who, that or whose belongs to the noun or clause before it, so it cannot start a new sentence. Replace the period with a comma. Where the reference is to a whole clause rather than a noun, supplying a noun is better still: a decision that explains the drop.

Openers like for example, such as, especially, including, particularly introduce a phrase, not a sentence, so what follows still needs its own subject and verb. Either give it one, or attach the phrase to the sentence before it with a comma or a dash.

Two complete clauses running together with no punctuation. Length is not the test \u2014 a long sentence can be perfectly built and a short one can be fused. Find every subject-and-verb pair, then check that something separates each pair from the next.

The most common boundary error in student writing, because a comma feels like enough. It is not. Four repairs are available: add a coordinating conjunction, change the comma to a semicolon, break into two sentences, or subordinate one clause. Which you choose depends on how closely the two ideas are linked.

Only seven words can join two independent clauses after a comma: for, and, nor, but, or, yet, so. Nothing else works in that slot. If the word you want is not on that list, you need a different repair.

A semicolon joins two clauses that are closely related, with no conjunction needed. When a linking adverb follows it, the punctuation is fixed: semicolon before, comma after. The same adverb can also open a fresh sentence \u2014 The results were inconclusive. However, the team repeated the trial.

However, therefore, moreover, nevertheless, furthermore, consequently, thus, otherwise, instead are adverbs. They comment on the relationship between two clauses but cannot join them, so a comma in front of one produces a splice. This is the single most frequent version of the comma splice in academic writing, because the vocabulary is academic and the punctuation looks deliberate.

Often the best repair, because it says how the two ideas relate rather than merely separating them. Turning one clause into a dependent one with after, because, although, since, when, while also varies the sentence rhythm, which raters notice in the writing tasks.

English uses one connector where Portuguese allows a pair. Although … but, because … so and despite … however are all doubled. Pick the subordinator or the coordinator and delete the other. This is among the most reliable markers of a Portuguese-speaking writer.

A comma before and signals that a second independent clause is coming. If the second half has no subject of its own it is a compound predicate, not a clause, and the comma is wrong. Check what follows the conjunction: a bare verb means no comma.