Learning to thinking clearly is “simply” a matter of unfailingly diligent mental hygiene.
- Don’t mix strong emotions with intellectual thinking (this is basic)
- Keep your identity small
- Identify all the unseen premises
- Don’t assume (especially, never assume you can’t understand something)
- HARD but indispensible: Avoid the myriad traps that words create through their vagueness - especially equivocation-based errors. This means always relentlessly seek out clearer and clearer definitions for all strategic terms upon which an argument rests.
The master key that unlocks all of the above is to divorce your intellectual thinking from your social signaling and the authority structure of society. This means way more than just demanding sources! Here’s a quote I liked regarding authority:
Though most will find the anti-mainstream physics examples bizarre, similar examples could be made regarding the errors of the statist attitudes of political scientists or mainstream economists. The key is that it is not merely wrong facts you have to watch out for, but the positive social association with careless thinking and language-usage habits that comes from listening to a revered authority figure make a bad argument that sounds very good.
For the child, then, the best way not to get them mired in the bad thinking habits of authorities is probably to not present anyone to the child as an authority; each person must rise or fall on his or her own coherence and clarity of explanation. No teacher or famous dead dude is any better than a random forum poster or a friend on the playground unless they can make a case clearly and have good mental hygiene habits.
Beyond that, all there is to do is let their natural curiosity bloom.