cf. Note on Chapter iii. p. 4.  In the Aristotelian philosophy, εἶδος, or Forma, is the τὸ τί ἦν εἶναι, the essence or formal cause.  cf. Ar., Met. vi. 7, 4.  εἶδος δὲ λέγω τὸ τί ἦν εἶναι ἑκάστον καὶ τὴν πρώτην οὐσιαν.  Δύναμις, or Potentia, is potential action or existence, as opposed to ἐνέργεια, actus, actual action or existence, or ἐντελέχεια.  cf. Ar., Met., viii. 3, 9, and viii. 8, 11.  Sir W. Hamilton, Metaph. i. 178–180.