What is political tyranny, Plato has Sokrates ask in the Republic, if not the unjust rule of a man who himself is tyrannized by his basest desires?
Is causative used in this sentence? I understand causative for example in this sentence: I'll have him call for the parcel. I will use my authority or influence and make someone do something. But is the same pattern possible in my sentence? Or is it there only expressed the fact that Plato speaks by means of Sokrates in his writings?
This use of has (as in I had my car repaired, I had my hair cut) is usually "causative" in the sense that the subject actively and deliberately arranged for someone else to repair his car, cut his hair, etc.
But note that there are similar contexts where the subject didn't deliberately arrange the outcome...
John had his nose broken in a pub brawl.
John had his house flooded by storm Desmond last week.
You probably wouldn't be misled into thinking John deliberately arranged for those outcomes, but any possibility of ambiguity can be resolved by John's nose was broken..., John's house was flooded...
In OP's exact context undoubtedly Plato acted deliberately, though there's still a small ambiguity...
a) The Republic faithfully reports a discussion between Plato and Socrates, within which Plato "steered" the conversation in such a way that Socrates had (was compelled) to ask the question.
b) Regardless of whether Socrates ever actually asked that question, it suited Plato's purposes to have (make) it seem as if he did, for the purposes of his presentation.
But to be honest I don't think it really makes much difference when we get to that level of detail.
Turning to OP's example I'll have him call for the parcel, it's worth pointing out that such usages are slightly "formal, dated". Idiomatically, people are more likely to say something like I'll get him to call for the parcel today.
Further to that, I'll also mention the (perhaps purely personal) opinion that using have rather than get carries stronger connotations of "imperiously" commanding that someone do something. Perhaps that's by association with he will have to [act in accordance with my wishes], or perhaps it's just because the usage is more formal, and thus associated with contexts involving "authority".
Thus, if we compare Can you get him to / have him do it?, for example, the get version will often be suitable in contexts where all you can actually do is ask him to do it - whereas the have version pragmatically requires that you have the power to force him to comply (if not, it's a misuse).
