I don't know if you guys have seen the British comedy quiz show QI (brilliant show), but in episode 10 of series A (aptly called Aviation) Stephen Fry (the host) mentions that there are five leading theories of how lift is generated, but none are validated. he then goes on to say that this only affects out understanding of lift and not how we engineer wings.
Now I am aware of maybe two prevalent theories (Bernoulli's principle and Coanda Effect), what are the other three he is referring to? And would an approximate theory (or an empirically sound hypothesis) be enough to design aircrafts?
Edit: I am aware of the fact that our understanding of lift is pretty watertight. I just wanted know if there were other hypotheses that used to compete with our current theory. (They could have been proven wrong, I just wanted to know them)