The particle οὐ signals the opposite of a number of verbs of speaking, thinking and desiring. The negation is subsumed in the verb to such an extent that it is no longer experienced as a negation.
οὐκ ἀξιόω ‘to think beneath oneself’, οὐ δοκέω, οὐ κελεύω, οὐκ ἐάω, οὐκ οἴομαι, οὐ νομίζω ‘to forbid’, οὐκ ἐθέλω, οὐχ ὑπισχνέομαι ‘to refuse', οὐκ ἐπαινέω ‘to disapprove of’, οὐκέω ‘to prevent’, οὐ προσποιέομαι ‘to hide’, οὐ συμβουλεύω ‘to advise against’, οὐ φάσκω and οὐ φημί ‘to deny’
The negation οὐ is usually retained, even where the construction requires μή.
In Homer the word order is even less stringent. He has both οὔ φημι and φημὶ οὐ, as well as οὔ φημι οὐ.
Languages like English subsume the negation in such verbs as a prefix: οὐ φημί – Eng. I forbid – Lat. nēgō. Other Latin examples include nesciō 'not to know', nequeō 'to be unable' en nōlō 'not to want'.