You are working on a crossword puzzle and the grid shows _EAR. Without an additional clue you would not know whether the missing letter was a B, D, F, G, H, L, N, P, R, S, T or W. All this proves is that many English words have similar contructions with only one letter different, a fact exploited by certain prize puzzle constructors who devise fiendishly clever puzzles which appear to have two or more correct answers. Only by following their tortuous logic can you divine the acceptable solution.
Eckler, Faith W.
Word Ways: Vol. 19
, Article 10.
Available at: http://digitalcommons.butler.edu/wordways/vol19/iss4/10