Fox News legal analyst Gregg Jarrett and Harvard University Law School professor emeritus Alan Dershowitz joined 'Hannity' to discuss Michael Cohen taking the stand in New York v. Trump.

Michael Cohen raised his right hand on Monday in the Manhattan trial of Donald Trump and swore to tell the truth. It was a meaningless gesture.

Cohen has done it before and then proceeded to lie under oath. He went to prison for it after lying to courts, lying to banks, lying to Congress, and lying to the IRS. Yet, once again, Cohen insists that now he’s telling the truth. He wants jurors to believe him. This time.

Cohen presents a contradiction about truth and falsity. In philosophy and logic it’s known as the "liar’s paradox," and it bedevils juries whenever habitual liars take the witness stand and promise to tell the truth.

The paradox is this: if a liar indeed lied, then his admission of his lies is truthful. Unless, of course, he is lying about the lie and everything else. You can never really know. The search for truth becomes impossible. In a court of law where the central witness is a chronic fabulist, the "liar’s paradox" equals reasonable doubt.

NY V. TRUMP: COHEN TESTIFIES TO PAYING STORMY DANIELS FROM HIS OWN POCKET

It was on full display Monday when Trump’s one-time self-proclaimed "fixer" failed to connect the accused to any cognizable crime. But Cohen readily confessed that he often lied and bullied people. He also deceived his own client, Trump, by secretly recording him shortly before the 2016 election.

Without permission, Cohen then shared it with the publisher of the National Enquirer. It was a sleazy maneuver that would merit disbarment for breaching the attorney-client privilege. No matter. Cohen was long ago disbarred over his criminal convictions.

When the recording was played in court it seemed to help, not hurt, the defense. Cohen refers cryptically to payments made to kill a story, which is not a crime. Trump appears somewhat in the dark and is heard asking, "What financing?" Cohen assured him that he was taking care of everything. His boss didn’t need to know the details. "I’ve got it…I’m on it," said Cohen.

Manhattan District Attorney Alvin Bragg........

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