MORE: I will not take the oath. I will not tell you why I will not.

NORFOLK: Then your reasons must be treasonable!

MORE: Not “must be”; may be.

NORFOLK: It’s a fair assumption!

MORE: The law requires more than an assumption; the law requires a fact.

Robert Bolt (1924-1995) English dramatist

A Man for All Seasons, play, Act 2 (1960)
    (Source)

The 1966 film adaptation uses the same language.