In general the subject of the infinitive, if expressed at all, stands in the accusative; when the subject of the infinitive is the same as the subject or object of the governing verb, or when it has already been made known in the sentence, it is not repeated with the infinitive.1973
When the subject of the infinitive is the same as that of the governing verb, it is omitted, and a predicate noun stands in the nominative case.
Πέρσης ἔφη εἶναι
ἐγὼ οὐχ ὁμολογήσω ἄκλητος ἥκειν
a. The nominative is used when the infinitive, expressing some action or state of the subject of the main verb, has the article in an oblique case. Thus, τούτων ἀξιωθεὶς διὰ τὸ πατρικὸς αὐτῷ φίλος εναι
τοῦτο δ' ἐποίει ἐκ τοῦ χαλεπὸς εἶναι
b. The nominative stands usually in sentences with δεῖν, χρῆναι etc., dependent on a
ἡγούμην . . . περιεῖναι δεῖν αὐτῶν καὶ μεγαλοψυ_χότερος φαίνεσθαι
c. When the governing verb is a participle in an oblique case, a predicate noun usually agrees with the participle, and rarely stands in the nominative. Thus,
ἀπαλλαγεὶς τούτων τῶν φασκόντων δικαστῶν εἶναι
τὰ_ς ἀρχὰ_ς δίδωσι . . . τοῖς ἀεὶ δόξα_σιν ἀρίστοις εἶναι
A pronoun subject of the infinitive, if (wholly or partially) identical with the subject of the main verb, is generally expressed when emphatic, and stands in the accusative (cases of the nominative are rare and suspected); but the indirect reflexive σφεῖς stands in the nominative or accusative.
οἶμαι ἐμὲ πλείω χρήματα εἰργάσθαι ἢ ἄλλους σύνδυο
τοὺς δὲ Θηβαίους ἡγεῖτο . . . ἐά_σειν ὅπως βούλεται πρά_ττειν ἑαυτόν
a. After a preceding accusative with the infinitive, a second pronoun referring to a different person, and also subject of an infinitive, must also stand in the accusative whether or not it denotes the same person as the subject of the governing verb. Thus, ἀλλὰ νομίζεις ἡμᾶς μὲν ἀνέξεσθαί σου, αὐτὸς (see below) δὲ τυπήσειν; καὶ ἡμᾶς μὲν ἀποψηφιεῖσθαί σου, δὲ (
When the subject of the infinitive is different from that of the governing verb, it stands in the accusative; and a predicate noun stands also in the accusative.
νομίζω γὰρ ὑ_μᾶς ἐμοὶ εἶναι καὶ πατρίδα καὶ φίλους
τὸν γὰρ καλὸν κἀ_γαθὸν ἄνδρα εὐδαίμονα εἶναί φημι
A predicate noun takes the case of the subject of an infinitive itself dependent on a subjectless infinitive. Thus,
ἡμῖν δὲ ποιοῦσι δοκεῖν σφᾶς παντοδαποὺς φαίνεσθαι
Several infinitives may be used in succession, one infinitive being the subject of another:
περὶ πολλοῦ ποιούμενος μηδενὶ δόξαι ὑβρίζειν βούλεσθαι
When the subject of the infinitive is the same as the object (in the genitive or dative) of the governing verb, it is often omitted, and a predicate noun is either attracted into the genitive or dative, or stands in the accusative in agreement with the omitted subject of the infinitive. See cross1060-1062.
ἔξεστιν ἡμῖν ἀγαθοῖς εἶναι or ἔξεστιν ἡμῖν ἀγαθοὺς εἶναι
Λακεδαιμονίοις ἔξεστιν ὑ_μῖν φίλους γενέσθαι
The subject of the infinitive is often retained when it is the same as the (omitted) oblique object of the governing verb. Thus,
παρήγγειλε τὰ ὅπλα τίθεσθαι τοὺς Ἕλληνας
An indefinite or general subject of the infinitive (τινά, τινάς, ἀνθρώπους) is commonly omitted; and a predicate noun stands in the accusative. Thus, φιλάνθρωπον εἶναι δεῖ
δρῶντας γὰρ ἢ μὴ δρῶντας ἥδι_ον θανεῖν
The construction of the accusative with the infinitive seems to have originated from the employment of the infinitive to complement the meaning of transitive verbs; as in κελεύω σε ἀπελθεῖν
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].