 Then the account turns to action (praxis), where we find the kind of thought that deals with what is capable of change. The efficient cause of actions is choice (prohairesis). The cause of choice is desire (orexis) and reasoning toward an end (logos ho heneka tinos). Thought (dianoia) by itself moves nothing, only thought that is practical (praktikê) and for the sake of an end. So, practical thought (dianoia praktikê) belongs to the calculative part and pertains to practical truth; theoretical thought (theôrêtikê dianoia) belongs to the the scientific part and pertains to truth and falsity. In turn, practical thought governs productive (poiêtikê) action. The latter has an end separate from the action, i.e., the product; we will see that this kind of practical thought is  technê. Underlining the way action requires the two elements of the soul, Aristotle sums up by saying choice can be called intellect fused with desire (orektikos nous) or desire fused with thought (orexis dianoêtikê) (1139a17–1139b5). While this chapter suggests that the truth sought by practical thought is different in kind from the truth sought by theoretical thought—because their respective objects are different—it ends with the summary claim that attaining truth is the function of both parts of the rational soul; then he turns to the virtues which make the soul able to attain the truth.