"The fortepiano distinguishes itself from a modern piano in several respects: Among other things, it has a much less complicated mechanics than the modern piano. The modern piano was developed in the course of a changed aesthetics, to enable an as great as possible sound. As a result, many subtle shades of expression were lost. Indeed, a fortepiano does not sound as loud as a modern piano, but instead one has the feeling as a pianist, that the fingers control the strings more directly. This facilitates a subtler performance of, among other things, articulation, than modern pianists generally are used to. There are hardly any dynamic signs in Mozart and Haydn's expression marks, like forte, piano, crescendo, diminuendo and so forth, instead articulation slurs abound. In the case of Mozart and Haydn’s music, one ought to express accents through articulation and not so much through dynamics. If the finger lets go of the previous key before playing the next one, the listener hears the next tone as accentuated.
Many contemporary pianists neglect this, because of the ponderous mechanics of the modern piano. However, in this kind of music, constant dynamic accents sounds often very coarse. A further difference consists in the much shorter tone of the fortepiano compared to the modern piano. This explains why the handed down metronome marks in the case of slow movements - e.g. from Beethoven - appear to modern pianists generally too fast. The tone of the modern piano has a slower decay and therefore encourages slower tempi.
Furthermore, the modern piano builder considers it a virtue if all registers of the piano have the same tone quality, meanwhile previously, fortepiano builders wanted consciously that the different registers of the piano have a different tone quality, somewhat imitating a string quartet.
Whoever has learned to play on historical instruments, can use the acquired knowledge when performing on modern pianos."