The expression "by ear" usually refers to the ease with which a child picks out a tune on the piano, or the uncanny ease with which some people can just sit down at the piano and play whatever music is fashionable that week.
But I use those words to evoke the activity of the inner ear. This is more elusive as it is in constant shift between past and present hearing. There is definitely a clash between the way we are taught to conceptualize tone and the way we actually experience it. All notes on all instruments are not equivalent to all other notes. Period.
It may be that some people, recognizing the inconstancy of their perception of tone, unconsciously require of themselves that they keep tone in order by mechanical repetition.
