As the Greek modes formed the basis for the musical system of the church, so the Greek monochord is the type from which the monks evolved what they called the clavichord.  The monochord has a movable bridge, therefore some time is lost in adjusting it in order to get the different tones.  To obviate this inconvenience, a number of strings were placed side by side, and a mechanism inserted which, by pressing a key (clavis), would move the bridge to the point at which the string must divide to give the note indicated by the key.  This made it possible to use one string for several different notes, and explains why the clavichord or clavicembalo needed comparatively few strings.  This instrument became obsolete toward the end of the eighteenth century.

The other species of instrument, the harpsichord, which was invented about 1400, and which may be considered as having sprung from the clavichord, consisted of a separate string for each sound; the key, instead of setting in action a device for striking and at the same time dividing the strings, caused the strings to be plucked by quills.  Thus, in these instruments, not only was an entirely different quality of tone produced, but the pitch of a string remained unaltered.  These instruments were called bundfrei, “unbound,” in opposition to the clavicembalo, which was called gebunden, or “bound.”  The harpsichord was much more complicated than the clavichord, in that the latter ceased to sound when the key which moved the bridge was released, whereas the harpsichord required what is called a “damper” to stop the sound when the key came up; once the string was touched by the quill, all command of the tone by the key was lost.  To regulate this, a device was added to the instrument by means of which a damper fell on the string when the key was released, thereby stopping the sound.

We have now to consider the instrumental development of the Middle Ages.

An instrument of the harpsichord family which has significance in the development of the instruments of the Middle Ages is the spinet (from spina, “thorn”; it had leather points up to 1500), first made by Johannes Spinctus, Venice, 1500.  It was a harpsichord with a square case, the strings running diagonally instead of lengthwise.  When the spinet was of very small dimensions it was called a virginal; when it was in the shape of our modern grand piano, it was, of course, a harpsichord; and when the strings and sounding board were arranged perpendicularly, the instrument was called a clavicitherium.  As early as 1500, then, four different instruments were in general use, the larger ones having a compass of about four octaves.  The connecting link between the harpsichord, the clavichord, and the piano, was the dulcimer or hackbrett, which was a tavern instrument.  Pantaleon Hebenstreit, a dancing master and inventor of Leipzig, in 1705 added an improved hammer action, which was first applied to keyboard instruments by Cristofori, an instrument maker at Florence (1711).  His instrument was called forte-piano or pianoforte, because it would strike loud or soft.