TITLE: Dictionary Meaning of "Modus Ponens" and "Modus Tollens"
QUESTION [6 upvotes]: I wanted to understand modus ponens and modus tollens better, and I searched for its dictionary meaning.
Wikipedia says that modus ponens is Latin for "mode that by affirming affirms" and that modus tollens is Latin for "mode that by denying denies".
Now, English is not my first language, but I understand it enough and these definitions still don't make sense. What does "mode" mean? what is "by affirming affirms"? Can someone better simplify it in English for me?

REPLY [6 votes]: By ‘mode’ it means deduction rule, and  ‘affirms’ means asserts the truth  of some proposition.
They are the abbreviation of the Latin sentences modus ponendo ponens and modus tollendo tollens.
They're the deduction rules which justify the following reasonings, in ordinary language:

if $A$ implies $B$ is true and if $A$ is true, then $B$ is true (modus ponens),
if $A$ implies $B$ is true, and if $B$ is false, then $A$ is false (modus tollens).