When someone blamed Hecataeus the sophist because that, being invited to the public table, he had not spoken one word all supper-time, Archidamidas answered in his vindication 'He who knows how to speak, knows also when'.

You’ll know what to say when the time comes. That’s the art, eh? What to say, and when to say it. And the rest is silence.

A smart person knows how to talk. A wise person knows when to be silent.

Everything comes in time to him who knows how to wait.

Only he who knows how to speak can be silent.

Then he will talk—good gods! how he will talk!

he who knows himself is intelligent.

He who knows others is wise; he who knows himself is enlightened.

When a man knows what he is talking about, his voice crackles with authority.

The ability to speak exactly is intimately related to the ability to know exactly.

I can understand, when it's the speaking.

He will win who knows when to fight and when not to fight

We know how to speak many falsehoods which resemble real things, but we know, when we will, how to speak true things.

To speak well is part of living well.