It seems to me that Aristotle was, in fact, responding to the first 'rationalist in politics', Plato, who had initially confused theory and practice, in, for example, the myth of the cave, where the philosopher, because he has mastered theory, is entitled to come back to the masses and dictate practice to them. As Oakeshott commented upon this:
"The cave-dwellers, upon first encountering the theorist after his return to the world of the shadows [very well might be impressed] when he tells them that what they had always thought of as ‘a horse’ is not what they suppose it to be… but is, on the contrary, a modification of the attributes of God [and they will] applaud his performance even where they cannot quite follow it. [The cave-dwellers can appreciate the exotic pronouncements of the theorist, as long as he confines those pronouncements to their genuine field of applicability, ] but if he were to tell them that, in virtue of his more profound understanding of the nature of horses, he is a more expert horse-man, horse-chandler, or stable boy than they (in their ignorance) could ever hope to be, and when it becomes clear that his new learning has lost him the ability to tell one end of a horse from the other… [then] before long the more perceptive of the cave-dwellers [will] begin to suspect that, after all, he [is] not an interesting theorist but a fuddled and pretentious ‘theoretician’ who should be sent on his travels again, or accommodated in a quiet home."
As Aristotle's thought moved away from Plato's, he sought to explore the difference between theoretical and practical wisdom, to clarify where Plato had gone astray. I here quote from an excellent paper by Daniel Deveroux, "Particular and Universal in Aristotle's Conception of Practical Knowledge."
"Practical wisdom, as Aristotle understands it, is analogous not to medicine but to medical skill; it is practical both in aim and in efficacy, and it is self-sufficient in the same way as medical skill: the practically wise person has what he needs to achieve his aims" (1986: 494).
"Matters of health and conduct 'have no fixity,' and therefore it would be futile to attempt to formulate precise statements about how we should act in various situations. One must speak 'in outline' and 'not precisely'" (1986: 494).
"Such statements will at best be useful as rules of thumb; the experienced agent or doctor will be guided not so much by them as by his judgment of what is 'appropriate to the occasion'" (1986: 495).
So, we might define the ideologue this way: He is someone who, lacking in political experience, tries to turn these rules of thumb into hard 'principles' that will provide him with the unambiguous guide to proceeding that his lack of experience has denied him. Thus, contra Geoffrey Allan Plauche, principles, at least as understood by ideologues such as Rand or Rothbard, certainly do not have a place in Aristotelean practical reasoning. The proper role of a statement like "The government ought to respect property rights" is as a rule of thumb; yes, generally, it ought to, but there are clearly other times when to do so would be not practical wisdom but practical idiocy. (See 'Scenario 2' of this post for an example.) And that is just how someone as bright as Rothbard managed to arrive at positions as stupid as his belief that blackmail ought to be legal: by mistaking theory for practice and turning what ought to be seen as rules of thumb into a rigid ideology, he rendered himself incapable of sound practical thought.