37 We are told by Mnaseas that the Muses are the daughters of Tellus and Coelus; others declare that they are Jove's by his wife Memory, or Mens; some relate that they were virgins, others that they were matrons. For now we wish to touch briefly on the points where you are shown, from the difference of your opinions, to make different statements about the same thing. Ephorus, then, says that they are three in number; Mnaseas, whom we mentioned, that they are four; Myrtilus brings forward seven; Crates asserts that there are eight; finally Hesiod, enriching heaven and the stars with gods, comes forward with nine names.
If we are not mistaken, such want of agreement marks those who are wholly ignorant of the truth, and does not spring from the real state of the case. For if their number were clearly known, the voice of all would be the same, and the agreement of all would tend to and find issue in the same conclusion.
Source: Against the Heathen (New Advent)