Regarding the earlier seven-stringed scales which preceded this octave our information is scanty and somewhat obscure. The chief notice on the subject is the following passage of the Aristotelian Problems:

Probl. xix. 47 dia ti hoi archaioi heptachordous poiountes tas harmonias tÊn hypatÊn all' ou tÊn nÊtÊn katelipon: hÊ ou tÊn hypatÊn (leg. nÊtÊn), alla tÊn nyn paramesÊn kaloumenÊn aphÊroun kai to toniaion diastÊma; echrÔnto de tÊ eschatÊ mesÊ tou epi to oxy pyknou; did kai mesÊn autÊn prosÊloreusan [hÊ] oti Ên tou men anÔ tetrachordon teleutÊ, tou de katÔ archÊ, kai meson eiche logon tonÔ tÔn akrÔn?

'Why did the ancient seven-stringed scales include HypatÊ but not NÊtÊ? Or should we say that the note omitted was not NÊtÊ, but the present ParamesÊ and the interval of a tone (i.e. the disjunctive tone)? The MesÊ, then, was the lowest note of the upper pyknon: whence the name mesÊ, because it was the end of the upper tetrachord and beginning of the lower one, and was in pitch the middle between the extremes.'

This clearly implies two conjunct tetrachords—

tetrachord

In another place (Probl. xix. 32) the question is asked, why the interval of the octave is called dia pasÔn, not di' oktÔ,—as the Fourth is dia tessarÔn, the Fifth dia pente. The answer suggested is that there were anciently seven strings, and that Terpander left out the TritÊ and added the NÊtÊ. That is to say, Terpander increased the compass of the scale from the ancient two tetrachords to a full Octave; but he did not increase the number of strings to eight. Thus he produced a scale like the standard octave, but with one note wanting; so that the term di oktÔ was inappropriate.

Among later writers who confirm this account we may notice Nicomachus, p. 7 Meib. mesÊ dia tessarÔn pros amphotera en tÊ heptachordÔ kata to palaion diestÔsa: and p. 20 tÊ toinyn archaiotropÔ lyra toutesti tÊ heptachordÔ, kata synaphÊn ek duo tetrachordÔn synestÔsÊ k.t.l.

It appears then that two kinds of seven-stringed scales were known, at least by tradition: viz. (1) a scale composed of two conjunct tetrachords, and therefore of a compass less than an octave by one tone; and (2) a scale of the compass of an octave, but wanting a note, viz. the note above MesÊ. The existence of this incomplete scale is interesting as a testimony to the force of the tradition which limited the number of strings to seven.