From Nicomachean Ethics V.

ᾑ̂ ἐλλείπει διὰ τὸ καθόλου. του̂το γὰρ αἴτιον καὶ του̂ μὴ πάντα κατὰ νόμον εἰ̂ναι, ὅτι περὶ ἐνίων ἀδύνατον θέσθαι νόμον, ὥστε ψηφίσματος δει̂. του̂ γὰρ ἀορίστου ἀόριστος καὶ ὁ κανών ἐστιν, ὥσπερ καὶ τη̂ς ***Λεσβίας οἰκοδομίας ***ὁ μολίβδινος κανών: πρὸς γὰρ τὸ σχη̂μα του̂ λίθου μετακινει̂ται καὶ οὐ μένει ὁ κανών, καὶ τὸ ψήφισμα πρὸς τὰ πράγματα. τί μὲν οὐ̂ν ἐστὶ τὸ ἐπιεικές, καὶ ὅτι δίκαιον καὶ τινὸς βέλτιον δικαίου, δη̂λον. φανερὸν δ' ἐκ τούτου καὶ ὁ ἐπιεικὴς τίς ἐστιν: ὁ γὰρ τω̂ν τοιούτων προαιρετικὸς καὶ πρακτικός, καὶ

http://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus:text:...

In fact this is the reason why all things are not determined by law, that about some things it is impossible to lay down a law, so that a decree is needed. For when the thing is indefinite the rule also is indefinite, like the leaden rule used in making the ****Lesbian moulding****; the rule adapts itself to the shape of the stone and is not rigid, and so too the decree is adapted to the facts.

--------------------------------------------------
Note added at 59 mins (2005-07-31 13:10:59 GMT)
--------------------------------------------------

Λεσβιάς οικοδομίας για την ακρίβεια