One claim that you’ll regularly encounter once you start reading various contemporary works on the Greek Verb from NT scholars is the idea that Georg Curtius (1873 [English: 1883]) was the originator of the idea that Greek does not grammaticalize tense outside the indicative mood.

Con Campbell’s (2015) Advances in the Study of Greek is a representative source of the claim, though it isn’t limited to him and I’m certainly not criticizing him for making it—he might be simply defaulting to the same position as Fanning (1990, 9-10).

Here’s Campbell (2015):

The chief significance of Curtius’s scholarship was as the father of Greek verbal aspect studies. He was the first to argue that the Greek verbal system differs from Latin, and that temporal reference is limited to the indicative mood and is not a feature of the other moods (a fact taken for granted today) (Campbell 2015, 31).

The thing is, I have no idea whether the claim is right or wrong. On the one hand, I’ve never seen in the grammars that I’ve searched anyone make the outright statement of the belief that temporal reference is possible outside the indicative. On the other hand, I certainly haven’t read everything…particular the substantial amount of 19th c. German scholarship.

Fanning cites Georg Curtius (Die Bildung der Tempora und Modi im Griechischen und Lateinischen sprachvergleichend dargestellt [Berlin: Wilhelm Besser, 1846], 148-52) as the source of the attribution of the idea to Curtius, when he writes:

The breakthrough to a different approach under the influence of comparative philology began with the work of Curtius, who was perhaps the first to attempt a union between the new comparative linguistics and Greek philology as it was more traditionally conceived. In an early book (1846), Curtius argued that, in contrast to Latin, temporal meaning is limited in Greek to the indicative mood and a different type of meaning is expressed by the present and aorist verbal stems: that of durative vs. ‘quickly-passing’ action (Fanning 1990, 10).

Fanning then goes on to cite Curtius’ observed distinction between: ἐγίγνετο from γίγνομαι, ἐγεγόνει from γέγονα.

It’s just that already in 1835 Raphael Kuhner effectively made the same distinction (1835, 62, my translation below):

	Present.	Past.	Future.
I. Absolute	γράφω	ἔγραψα.	γράψω.
II. Relative a. Simultaneous Duration	γράφω.	ἔγραφον.	γράψω.
b. Finished	Γέγραφα	ἐγεγράφειν	γεγραφὼς ἔσομαι.
c. Upcoming Events	Μέλλω γράφειν.	ἔμελλον γράφειν.	μελλήσω γράφειν.

Now Kuhner’s approach to the verb isn’t exactly standard compared to what we have today, but it is certainly clear that he recognizes that past tense is morphologically connected to the augment and thus secondary indicative forms. Moreover, he goes on to explicitly state that for the infinitives and participles, temporal reference is only available with reference to either the speech time of the speaker or some other action. And when we move to the moods, we find no reference to temporal reference at all!

So maybe, at best, Curtius is the first one who explicitly stated the fact that tense is contained to the indicative mood, but I’m inclined to think that he isn’t the origin of the idea. It seems to have already been well established.