Discussion is externalized thinking. Thinking is self-discussion.
Not entirely. This mostly applies to the conscious aspects of thinking. It’s thinking that you pay attention to, not autopilot/habits.
Rational critical analysis looks at the content of ideas, not their sources. It doesn’t matter if the source is you or someone else, it’s the same idea either way. The same sort of analysis needs to be done to evaluate two rival ideas regardless of their sources – which means, regardless of whether they come from two different people in a discussion or from one person who is thinking silently.
Discussion lets other people share criticism with you and learn from you. Those are big benefits. They help share good ideas and overcome people’s personal weaknesses. Some of your weaknesses are not shared by some of your discussion partners, and you don’t have some of their weaknesses, so there’s lots of scope to help each other.
Good thinkers can think out loud and can think as part of discussion. They don’t have to think alone first, in advance of discussion. They can do some thinking in real time, and some in fairly near real time (writing a text reply slower than talking out loud as one thinks, but without taking any significant break to think things over).
People who have trouble thinking in discussion also have trouble thinking outside of discussion. But there are some important differences. People who get pressured and socially manipulated a lot can think better alone because those things happen less when there isn’t another person directly involved. But if they were a better thinker they’d deal with that better.
Many people believe they know an idea, they just can’t explain it well. They separate thinking and communication as different skills. But if you can explain the idea to yourself, you can use that same explanation with other people!
People also claim they have arguments that convince themselves but wouldn’t convince you. This is biased. They believe it’s because they have access to information that you don’t, e.g. their own internal feelings or memories. But they can tell you those. You and they should both see the evidence the same way: “Joe reports remembering X.” or “Bob says that he feels Y very strongly and seriously.” The reason they think it’s more convincing for them, than you, is they realize that those kinds of reports are unreliable and you won’t accept it, but they believe those kinds of reports, anyway, when they are the reporter. That’s biased and bad thinking. People should learn to be skeptical of their own beliefs. If they know they have a belief that a reasonable external person would be skeptical of, they should doubt it themselves, too.
People also separate truth-seeking and debating as different skills. They think the better thinker, with the better idea, can lose a debate because he is less good at clever rhetoric. This is reasonably accurate when both thinkers aren’t very good. But great thinkers can handle these issues. A good thinker can point out rhetoric, manipulation, faking, etc. A good thinker will refocus the discussion on key points like what are the criticisms of each idea, and ask the other person to cooperate in joint truth-seeking. The gullible people in the audience may still be fooled, but that should clarify matters enough for the reasonable people to be able to see what’s going on. (Of course errors can always happen. There are no guarantees.)
All this means: learning to discuss is a way of learning to think well. And learning to think well without learning to discuss well is implausible and is a sign of fooling yourself. Because thinking and discussion are linked, and most genuine skill at either one also works for the other.