Porter would have us believe that the the Greek Future tense is aspectually vague. That is, it does not participate in the perfective/imperfection system in any way.

I have argued in a past post (see that post both for reference to Porter’s discussion as well) that the best way of explaining the Future is that it forms a pair with the aorist in the same way that the imperfect forms a pair with the present. The benefit of this claim is that it solves the challenge of why the future for the most part does not appear in the oblique moods. It does not just as the imperfect does not. There is also a morphological parallel in that both the aorist and the future contain a –σ.

These are synchronic arguments. I’d like to put forward a diachronic argument here, if only in a sort of outline format.

• It it generally agreed that the Greek future developed from the Aorist Subjective. The reference grammars are in general agreement on this point.
• The Modern Greek future developed from the verb θέλω with an infinity (I want to X) which was over time shortened to θα with the indicative (I will X).
• Modern Greek makes a distinction between the imperfective and perfective aspects in the Future:
  • Imperfective Aspect: εγώ θα ακούω… (I will be hearing… )
  • Perfective Aspect: εγώ θα ακούσω… (Ι will hear …)

Note that the difference between the Future Imperfective and the Future Perfective in Modern Greek continues to be the Sigma Suffix.

No matter how possible it could be, it does not at all seem plausible to me that a verb form that developed from the Aorist Subjective (which by definition is aspectually perfective) would lose its “perfective-ness” for the Koine Period only to regain it again in late Medieval and Modern Greek with the very same –σ suffix.