I've always read it as F. How can you rule out the possibility that, before certain advances in dental technology [1], most people spoke with a lisp, so what y

I've always read it as F. How can you rule out the possibility that, before certain advances in dental technology [1], most people spoke with a lisp, so what you read is what would have actually been said? It's not like there are recordings or standardized international phonetic alphabets to record the sounds represented by the letters. [1] I seem to remember George Washington's dentures a technological marvel of his day, or something.