MODUS PONENS: Latin MODUS "standard, measure" is from the Indo-European
root MED- "to take appropriate measures." The second word, PONENS, is
the present participle of Latin PONERE "to put." (See more under
COMPONENT.) In logic, MODUS PONENS is a standard form of argumentation
in which you "put down" the antecedent of an if-then statement and
conclude the occurrence of the consequence of that if-then statement.
MODUS TOLLENS: ... The second word, TOLLENS, is the present participle
of Latin TOLLERE "to take away," from the Indo-European root TELE- "to
lift, support." In logic, MODUS TOLLENS is a standard form of
argumentation in which you "take away," that is, negate, the consequent
of an if-then statement and conclude the negation of the antecedent of
that if-then statement. MODUS TOLLENS is equivalent to using the
contrapositive of the original if-then statement.