Ἐπιστήμη, insofar as it is a task to be carried out, is itself a πρᾶξις, admittedly one which does not have as its goal some sort of result (the way producing does) but instead simply strives to get hold of beings as ἀληθές. The task and the goal of ἐπιστήμη is thus to know the ἀληθές. Initially and for the most part, however, this knowing is in service to a making. Ἀληθεύειν contributes to the carrying out of a ποίησις or a πρᾶξις.
For ἀληθεύειν is indeed not the only determination of the ψυχή. It is merely a particular possibility (though, to be sure, a constitutive one) of a being which possesses the character of life (ψυχή): namely of that being which is distinguished by the fact that it speaks. Aristotle characterizes quite generally the two basic possibilities of the soul (ψυχή) as κρίνειν and κινεῖν. The αἴσθησις of the animal already has the character of κρίσις; even in αἴσθησις, in the natural act of perceiving, something is set off against something else. The second determination is κινεῖν, "to bestir oneself." To this corresponds the higher determination of the Being of man: πρᾶξις, κινεῖν in the sense of κρίνειν, in the sense of distinguishing things in speech. The ζωή of man is πρακτικὴ μετὰ λόγου.2 It is characterized by πρᾶξις καὶ ἀλήθεια (cf. Nic. Eth. VI, 2, 1139a18), i.e., by πρᾶξις, acting, and by ἀλήθεια, the uncoveredness of Dasein itself as well as of the beings to which Dasein relates in its actions. Both these basic determinations—with regard to the possible ways they may manifest themselves—can be termed: αἴσθησις, νοῦς, ὄρεξις. Thus Aristotle says: the κύρια, the dominant possibilities of every human comportment, are: αἴσθησις, νοῦς, ὄρεξις. τρία δή ἐστιν ἐν τῇ ψυχῇ τὰ κύρια πράξεως καὶ ἀληθείας, αἴσθησις νοῦς ὄρεξις (a17ff.).
Every comportment of Dasein is thus determined as πρᾶξις καὶ ἀλήθεια. In the case of ἐπιστήμη, scientific knowledge, the character of the πρᾶξις did not explicitly come out because, in science, knowledge is autonomous and as such it is already πρᾶξις and ὄρεξις. In the case of τέχνη, however, the ἀληθεύειν is that of a ποίησις; τέχνη is a διάνοια ποιητική (a27f.), a thorough thinking about beings that contributes to producing something, to the way in which something is to be made. Therefore in τέχνη, as ποίησις, and in every πρᾶξις, the ἀληθεύειν is a λέγειν which ὁμολόγως ἔχον τῇ ὀρέξει (cf. a30), "which speaks exactly as ὄρεξις desires." It is not a theoretical speculation about beings, but instead it expresses beings in such a way that it provides the correct direction for a proper production of what is to be made. In this way the ἀληθεύειν in τέχνη and φρόνησις is oriented respectively toward ποίησις and πρᾶξις.
2. Cf. Nic. Eth., I, 6, 1098a3ff.