Close on four dozen features under his belt, and on the cusp of his ninth decade on earth, Woody Allen grows understandably ever more inconsistent. Flashes of the old brilliance pop up here and there, while clunker lead balloons are more apparent and frequent, as in Irrational Man.

The writer-director knows his history and stuff, and philosophy professor Abe (Joaquin Phoenix) ought to know his. The latter's class and personal discussions of his area of expertise unfortunately are gobbledegook that gives Allen free rein to indulge himself. Little noted earlier in much better works was a penchant to lecture from on high: "so self-righteous . . . you think you´re God" (that very Deity, in fact, being the title of a 1975 one-act play of his).

He long ago instructed us "why life is worth living," something this current hero has not been able to formulate even dreamt of in heaven and earth in his philosophy. Feckless, a bit hangdog, to the point of physical and emotional impotence, he has nevertheless written so cunningly, we are to believe, as to cover up this moral bankruptcy and be hired as the newest, highly viewed staff member of a college in Rhode Island.

Hip flask frequently pulled out for a sip, he is also intriguing enough to attract the attentions of lonely biology lab teacher Rita (Parker Posey), who throws herself at him. At the same time, he becomes fast friends with his best student, Jill, who lives with her parents there in Providence and has a loving boyfriend in Roy (Jamie Blackley) but nevertheless falls for her prof, too. Emma Stone strikes one as just a smidgen too old and experienced to be this student too innocent to realize that, especially in a small closed community, her constant attendance on Abe will lead to problems. Remarkably, no one else notices anything, either, while he should clearly know better, especially after turning down her initial overtures.

Too late in the game, and in the ninety-five-minute script, Abe comes up with and carries out an out-of-thin-air existential act, thus in theory creating himself. In this sudden taking the bull by the horns, he goes from lackadaisical to fond endowed lover, from apathy to draining life to the fullest.

But the man has overreached himself, murder will out, as, in a weak Hitchcock-Roald Dahl denouement, the consequences of his supposed act of assertion of freedom lead deeper into a cul-de-sac requiring more. Fate is not the same as chance in, say, his hollow theatrical Russian roulette bit, but, rather, is the result of conscious choice.

Incessantly to a Ramsey Lewis score that quickly goes from memorable to overused, the mystery is why Allen bothered to do this movie in the first place. To keep his hand in, one might suppose but wishing he had abstained

(Released by Sony Pictures Classics and rated “R” for some language and sexual content.)