why do i have a midterm in the 3rd week. not logical.

[inconvenienced]

a argument is valid if and only if the set of sentences consisting of its premises plus the negation of its conclusion is inconsistent.

only sentences are tue or false.
only sets of sentences are consistent or inconsistent.
only deductive arguments are valid or invalid.
only inductive arguments are strong or weak.

deductibly valid - if the premises are all true, the conclusion cannot be false.
sound argument - a deductibly valid argument with true premises.

if you can reduce your argument to a valid form, then your argument is valid.

modus ponens
if circle then square,
circle,
therefore square.

modus tollens
if circle then square,
if not the case of square,
therefore not the case of circle

fallacy of denying the antecedent
if circle then square,
not circle,
therefore not square

fallacy of affirming the consequence
if circle then square,
square,
therefore circle