Feynman confused pedagogical skill with expertise in a given field. He insisted that experts could explain things. No, that's what a teacher does. Feynman was good at both and apparently had no one to challenge him on his claim that they were the same.
It's possible to be a great teacher without being an expert on given subject matter. And it's possible to have the most expertise but be inscrutable.
In the case of this quote, Feynman wasn't talking about expertise at all, but about explaining a thing with enough relevant details to be understood. Without those, a layman would not understand either.
From my experience “experts” who are unable to explain well typically have an incomplete understanding.
Language and knowledge are linked to a degree.
Personally I have had subject I thought I was an expert an and when I went to explain them I realized the shortcomings of my understanding. Later when I was truly an expert my ability to explain them improved.
> From my experience “experts” who are unable to explain well typically have an incomplete understanding.
You also have to give yourself permission to step several tiers back and think about how to distill "next pieces" into what they know.
I also find myself handwaving away a whole lot of edge cases or rigor away in order to have a bite-sized step that will help the student make progress.
> Personally I have had subject I thought I was an expert an and when I went to explain them I realized the shortcomings of my understanding. Later when I was truly an expert my ability to explain them improved.
Conversely, I find every time I've done this exercise of stepping back and breaking it down for someone else, my knowledge has deepened.
My biggest challenge with explaining things to people is the stuff they already know that's either wrong or not relevant. To save the effort of finding out later, I now ask people to explain it to me first, tell me everything they know about this, before I can figure out how far back I have to step before explaining it all.
I'm also a "What do you think happens?" person. It both gives me a place to start, and a bunch of stuff to peg other stuff onto that I'm about to say. If you can link points of a good explanation to points of a bad, but intuitive naïve explanation, it makes it easier to remember the good explanation.
That is the the special skill of a teacher. But any expert should be able to competently explain something to someone who isn't harboring a mistaken belief.
I think the ability to explain well requires you to be an expert, but also be able to quickly trace back all the definitions to what your student already knows.
Feynman was not a great teacher. Lots of people love his lectures now. But they're not getting graded on it.
Actual students were considerably more mixed. Obviously individuals vary so if I post how most of his students were totally lost in class, they'll post how one student went on to win a Nobel prize and say gotcha.
There are two types of teaching. One is teaching things to a complete beginner. The other is teaching things to someone who has already mastered the mechanics of a subject.
Feynman was a world class second type teacher. If you already know how to work with physics equations and solve problems, then Feynman's lectures will improve your understanding considerably. The simplification process he does, gives you a grand understanding of the theory.
Due to this, much of Feynman's pedagogy is not suitable for the first type of teaching. And should not be used as such.
This reminds me of University Physics by Young and Freedman. The things I already understood were really dumbed down, and the things I didn't understand were inscrutable. I ended up using it as a door stop for the rest of the year until it fell apart and I had to throw it away. It was one of the first ones where the book came with a code that you had to use online to do the homework, so the book was also useless as second hand, after being useless when bought new.
It's possible to be a great teacher without being an expert on given subject matter. And it's possible to have the most expertise but be inscrutable.
In the case of this quote, Feynman wasn't talking about expertise at all, but about explaining a thing with enough relevant details to be understood. Without those, a layman would not understand either.