Gerund phrase

A gerund phrase is a verb in its -ing form acting as a noun, together with anything it governs — 'rowing against the current' — so the whole phrase can serve as the subject or the object of a sentence.

Rowing against the current exhausted them. The phrase is the subject of that sentence: you could replace the whole thing with the work and the grammar would still hold. That substitution test is what identifies a gerund phrase. If a noun fits in its place, it is a gerund.

This matters for one practical reason. An -ing phrase can also be a participial phrase, which modifies a noun instead of being one, and the two look identical on the page.

• Rowing against the current, they made no progress. — participial; it modifies they.
• Rowing against the current made no difference. — gerund; it is the subject.

Only the second kind is safe from a dangling modifier, because it is not attached to anything that could go missing.

The editorial caution is the one that also applies to hidden verbs: a gerund converts an action into a thing, and a paragraph built on gerunds — the waiting, the checking of the road, the not knowing — goes static. Used once, deliberately, that stillness is the effect. Used throughout, it is just a page where nothing moves.