"[Diogenes of Sinope] used to say, that there were two kinds of exercise: that, namely, of the mind and that of the body; and that the latter of these created in the mind such quick and agile phantasies at the time of its performance, as very much facilitated the practice of virtue; but that one was imperfect without the other, since the health and vigour necessary for the practice of what is good, depend equally on both mind and body. And he used to allege as proofs of this, and of the ease which practice imparts to acts of virtue, that people could see that in the case of mere common working trades, and other employments of that kind, the artisans arrived at no inconsiderable accuracy by constant practice; and that any one may see how much one flute player, or one wrestler, is superior to another, by his own continued practice. And that if these men transferred the same training to their minds they wou1d not labour in a profitless or imperfect manner." - Diogenes Laertius.