The answer is COGENT, six letters. Cogent describes an argument or piece of evidence strong enough to compel agreement, which is what convincing means when the clue is read as an adjective. If six squares will not take it, try CREDIBLE at eight, PERSUASIVE at ten or the rarer SUASIVE at seven.
Cogent means driven together
English borrowed cogent in the 1650s, by way of French, from the Latin verb cogere. That verb was built from com, together, and agere, to drive, so its literal sense was to drive together. In Latin it could mean to collect, to compel or to curdle, and the curdling sense survives in coagulate, which comes from the same verb. Picture milk solids being pushed into a clump and you have a fair image of what a cogent argument does to loose points.
The English word kept the compelling sense. At its core, cogent means compelling assent or conviction, which puts the weight on the reasoning rather than on the person doing the arguing. That is why it sits so neatly under this clue. A charming speaker can win a room with a weak case, but an argument is only cogent if its points push the listener toward the conclusion.
Convince once meant conquer
The clue word has a combative history of its own. Convince arrived in the 1520s meaning to overcome in argument, from Latin convincere, to overcome decisively, which is built on vincere, to conquer. The same verb gave Latin victoria, the source of English victory. The gentler sense, to persuade firmly by argument or evidence, dates from around 1600. The Century Dictionary in 1897 drew a line that still helps: to convince someone is to satisfy their understanding that something is true, while to persuade them is to move their will.
Setters use both families. PERSUASIVE and SUASIVE come from Latin suadere, to urge or advise, the same verb behind dissuade. Suadere literally meant to recommend something as good, and it traces back to an ancient root meaning sweet or pleasant, the same root behind the Latin word for sweet. SUASIVE has been in English since about 1600 and is rare in conversation, but it is on record as a seven letter answer here.
Persuasion words sorted by blanks
| Letters | Answer | When it fits |
|---|---|---|
| 4 | REAL | Older grids, in the sense of true to life |
| 5 | VALID | The clue leans on logic or law |
| 6 | COGENT | The default at six |
| 6 | POTENT | The argument lands with force |
| 7 | SUASIVE | Rare and formal, but on record |
| 8 | CREDIBLE | The clue leans on belief or trust |
| 10 | PERSUASIVE | The plain long form |
| 10 | SATISFYING | An explanation that settles the question |
Valid and credible answer different questions
When crossings leave two candidates standing, the meaning can break the tie. VALID comes from Latin validus, strong or effective, and its first English sense in the 1570s was legally binding. Logicians use it narrowly: a deductive argument is valid when its form makes it impossible for the premises to be true and the conclusion false. A valid argument can still reach a false conclusion if one of its premises is false, which is why valid alone is not quite the same as convincing. CREDIBLE comes from credere, to believe, and describes something worth believing, so it suits a witness or a story as much as an argument. POTENT, from the Latin verb for being able or powerful, the same verb behind possible, is about force rather than logic. It also shares four of its six letters with COGENT, including the whole ENT ending, so at six squares only the first or third square will separate the two.
Reading the clue as an adjective
The ending on the clue can pull you toward a verb. Convincing could describe the act of talking someone round, but the answers recorded for this clue are adjectives, from REAL to SATISFYING. Treat the clue as describing an argument, a performance or a piece of evidence, and match the length. If your crossings insist on an ING ending, the setter has taken the verb route, and the safest move is to solve the crossing entries first rather than guess at a synonym.
