Correct fingering is a very essential part of piano playing, for it not only conduces to an easy supple technique and to the proper performance of the music, but it also assists in giving light and shade to passages.
This is because some of the fingers are stronger by nature, and some are weaker, and by using them according to their different strength when required, a certain natural gradation of tones is thereby generated.
In the early days of pianoforte playing it was considered wrong to use the thumb or the 5th finger at all upon the keyboard, and later when these two were admitted it was still forbidden by teachers to take a black key with the thumb, and this even until quite a short time ago.
The reason that the use of the thumb was thus limited was partly due to the fact of its working rather awkwardly on the black notes owing to its construction. But the main objection to it really was that it was impossible to get a legato tone on the black keys if the thumb was employed. This would be so still if it were not for the help of the pedal; but until recently the pedal had not reached the perfection of mechanism which it now enjoys, and was consequently not applied so much. At any rate people did not think of using it to facilitate the free employment of the thumb. ‘Nowadays, of course, even jumps can be bound over by the skilful application of the pedal, and a smooth, flowing, continuity of tone can be obtained in the most awkward passages.