(quoting Irene) Perhaps we should search for some?
χαῖρε φίλε, χαῖρε φίλη!
Here are two:
John 3:7 used the aorist:
μὴ θαυμάσῃς ὅτι εἶπόν σοι, Δεῖ ὑμᾶς γεννηθῆναι ἄνωθεν.
John 5:28 used the present:
μὴ θαυμάζετε τοῦτο, ὅτι ἔρχεται ὥρα ἐν ἧ πάντες οἱ ἐν τοῖς μνημείοις ἀκούσουσιν τῆς φωνῆς αὐτοῦ
What's the difference in meaning between these two? Look, I'm not denying that, IF THE CONTEXT SUPPORTS IT, there can be a difference. IF THE CONTEXT SUPPORTS IT, we could say that in the first instance Jesus is objecting to a short, punctiliar amazement, whereas in the second instance, Jesus has in mind an amazement that would last longer. Or it's possible, IF THE CONTEXT SUPPORTS IT, that in the first instance Jesus is stopping Nicodemus from doing something that he has not started yet, whereas in the second place the Judeans have already begun to marvel. Or, IF THE CONTEXT SUPPORTS IT, we can say that in the first instance Jesus is giving a specific prohibition limited to one occurrence, while in the second instance Jesus is banning something in general that he expects to be an on-going problem.
But the context supports none of these distinctions. And if the context did, we would not need the tenses to provide this information. I think that Smyth puts it best:
Smyth, Greek Grammar, 1841e:
The distinction (between μὴ γράφε and μὴ γράψῃς) is often immaterial, often a difference of tone rather than of meaning; sometimes too subtle for dogmatic statement.
I call this approach to Greek grammar semantic minimalism. I'm not denying that there are some general guidelines about the tenses that one can learn from the textbooks, but applying these to any actual instance of real Greek almost always involves reading more meaning into a passage than the author intended. If we tried to do this with a language that we know really well, like say, English, we would immediately realize that we are going astray. I have heard, as I'm sure you have, Uberdwayne, different preachers express the idea behind 1 John 2:15 in different ways. One guy might say
Don't start loving the world, now.
Another guy might say
I want you to stop loving the world!
Now, if you stopped and analyzed each word, you would realize that different constructions are used, and you could infer that in the first instance the preacher is talking to people who have not started to love the world and in the second instance the audience has already started to love the world. But think about it. Grammar aside, does this distinction make any sense? Is there any Christian who is in danger of loving the world, but has not started loving it? Of course we have here just two different manners of expressions that are saying the same thing. What we would not do to English I see no reason to do to Greek.
βούλομαι δὴ ὑμῖν ἐρρῶσθαι!
I am writing in Ancient Greek not because I know Greek well, but because I hope that it will improve my fluency in reading. I got the idea for this from Adrianus over on the Latin forum here at Textkit.