Question regarding accentuation as seen in Λόγος

I’m working through Λόγος by Santiago Carbonell Martinez alongside Athenaze and other resources following the method outlined by Ranieri and Roberts and have a question regarding accentuation that I cannot seem to understand.

As an example, in these sentences from κεφάλιον Α’: Πυθαγόρας θεὸς ούκ ἔστιν, άλλ’ ἄνθρωπος. Και Όρφεὺς ἄνθρωπός έστιν.

  1. Why are there two sets of accentuation for ἄνθρωπος /ἅνθρωπός
  2. Why are there different spellings for ἔστιν /ἐστιν

I’ve seen quite a bit of what I think is shifting accents but I’m not sure when this should happen, when it shouldn’t etc. Any guidance would be sincerely appreciated!

ἐστιν is usually enclitic, as in Όρφεὺς ἄνθρωπός ἐστιν (cf. ἄνθρωπός τις). But after οὐ it carries its own accent, οὐκ ἔστιν, as in Πυθαγόρας θεὸς ούκ ἔστιν (“P. isn’t a god”)—or so ancient grammarians say.

This is not to be confused with the dogma according to which “existential” ἐστι is orthotone, as in Πυθαγόρας ἔστιν “P. exists.” I don’t know if your book follows that practice.

Many thanks for the explanation! This makes more sense.