The other week I proposed 10 things everyone should know in or about philosophy. Judging by some people's reactions, perhaps I should've kept the two types separate. If you want a purely metaphilosophical list, let me recommend DuckRabbit. But I was also wanting to explore the question of which commonplace assumptions or 'folk beliefs' philosophical reflection should lead us to reject as false. In addition to those mentioned in my earlier post, a few other lessons spring to mind:
1) Not all actions stem from selfish motives. Sure, you can define "selfish" so that doing whatever you choose (hence, "want") counts as "selfish". But that trivializes the thesis -- it says no more than that actions stem from motives. So shut up with the knee-jerk cynicism already.
2) Rationality does not require always and only acting to advance your self-interest. I think this is pretty conclusively established by Parfit's arguments about incomplete relativity. We should either be instrumentalists or universalists about reasons. Rational egoism is an unstable and ad hoc intermediary position. (I suspect that most people who unthinkingly espouse this view are really instrumentalists who simply assume that people are purely self-interested in their aims. But see #1 above.)
3) Knowledge does not require certainty. We learn this from considering Matrix-like skeptical scenarios.
4) Whether "a tree falling in an empty forest makes a sound" is not a profound problem. It's simple once you disambiguate the term 'sound'. The falling tree causes soundwaves, but no conscious experiences or sound qualia. End of story.
5) Deontological absolutism and moral objectivity are not the same thing! Most people seem to believe that if you deny that lying is always wrong, then you should be a relativist. That's stupid. One can (and should!) have context-sensitive moral principles, as in consequentialism, whilst still insisting that these principles yield the objectively correct answer in any particular situation.
(When you add this to the points made in my earlier post, it looks like most people are simply thoroughly confused about what objectivity actually involves. Most unfortunate.)
6) Pure self-creation is incoherent. Choice requires a prior basis which underlies judgment. Corollary: 'Nurture' requires 'nature' to guide it. A genuine 'blank slate' could do no more than a rock.
What other commonplace confusions and rational remedies can you think of?