Though the account of classes of causes and of their relation to τὰ ἐφ’ ἡμῖν given here [Aristotle  , Nichomachean Ethics III,3] is not very clear or straightforward, it still indicates that there is a class of things rightly called τὰ ἐφ’ ἡμῖν, covering both what happens by intellect (νοῦς) as well as all other things happening through man (καί πᾶν τὸ δι’ ἀνθρώπου). All of these qualify as things ‘which can be done’ (πρακτά). But, even more interesting is (iii), i.e. that they are things that happen through us, and not always in the same way, and (iv), i.e. that they are things that happen for the most part, but remain unclear as to how they will turn out, and things undecided. Distinct from this class, there are things happening through chance (τὰ ἀπο τύχης), i.e. things of which τύχη is the cause (αἰτία). Distinct from these two classes there are things happening through nature (τὰ φύσει), i.e. things of which nature (φύσις) is the cause (αἰτία), including some of the things that change but always happen in the same way. Finally there are things happening through necessity (ἐξ ἀνάγκης), i.e. of which necessity (ἀνάγκη) is the cause (αἰτία), also including some things that change but always happen in the same way. [Eliasson  ]