«ἐστὶ γνωρίζειν καὶ οὐδεμιᾶς ἐπιστήμης ἀφωρισμένης» (Aristotle, Rhetoric, 1.1)

Question

Aristotle, Rhetoric, 1.1:

ἡ ῥητορική ἐστιν ἀντίστροφος τῇ διαλεκτικῇ: ἀμφότεραι γὰρ περὶ τοιούτων τινῶν εἰσιν ἃ κοινὰ τρόπον τινὰ ἁπάντων ἐστὶ γνωρίζειν καὶ οὐδεμιᾶς ἐπιστήμης ἀφωρισμένης

I translate it thus:

The rhetorical [art] is antistrophic to the dialectical [art]
ἡ ῥητορική ἐστιν ἀντίστροφος τῇ διαλεκτικῇ

for both concern such things that are common in a certain manner to everyone
ἀμφότεραι γὰρ περὶ τοιούτων τινῶν εἰσιν ἃ κοινὰ τρόπον τινὰ ἁπάντων

My question concerns the phrase:

ἐστὶ γνωρίζειν καὶ οὐδεμιᾶς ἐπιστήμης ἀφωρισμένης

Here is what (I think) I know:

οὐδεμιᾶς, ἐπιστήμης, and ἀφωρισμένης all share the same declension (i.e., feminine, genitive, singular).

According to LSJ on the verb εἰμί (re: ἐστὶ),

ἔστι impers., c. inf., it is possible...

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Edit (11/14/2018@5:48 PM): I have revised my translation, as follows:

The rhetorical [art] is antistrophic to the dialectical [art], for both concern such things which are common, in a certain manner, of all people and are possible to know, not being limited to scientific knowledge.

Please critique for me please. I am attempting to keep it as close to the Greek as possible while still possessing sense.

Answer 1

ἐστὶ γνωρίζειν goes with the previous bit:

περὶ τοιούτων τινῶν εἰσιν ἃ κοινὰ τρόπον τινὰ ἁπάντων ἐστὶ γνωρίζειν

"they are about such things as it is possible to become acquainted with [as being] in a certain manner common to all"

Then οὐδεμιᾶς ἐπιστήμης ἀφωρισμένης may be a genitive absolute: "with no system of knowledge being distinct / specifically dedicated [to them]". Or perhaps better, as brianpck suggests in comments, it can be taken as parallel to ἁπάντων, "common to all and not to any distinct system of knowledge".