In deductive reasonings the conclusion derives necessarily from the premises, because the premises are taken as true and the reasoning follows logic rules.
A. Jonathan leaves for school at 7:30 a.m. and is on time. Jonathan will always be on time if he leaves at 7:30 a.m.
This is not a logical reasoning, because the fact that one time Jonathan leaves at 7:30 am and is on time is one case, which does not permit to drive a conclusion of the future.
B. The local grocery store charges $3 for a gallon of milk. Joe is going
to the local grocery store to buy milk. Therefore, Joe expects to spend
$3 for a gallon of milk.
This is a logical reasoning, because the premise is that the local grocery store charges (as a must, always) $3 for a gallon of milk, so Joe can conclude that this is what will happen when he goes to the local grocery store.
C. All three angles in an equilateral triangle measure 60°.
Triangle ABCTriangle ABC is an equilateral triangle. Therefore, all
three angles in triangle ABCtriangle ABC measure 60°.
This is also a logical reasoning, becasue the ABC triangle is a case of equilaterl triangle and so it has to meet the condition given in the premise: all the angles measure 60°.
D. Mary and Sue are friends. Mary enjoys fishing, running, and rock climbing. Sue likes fishing and rock climbing. Sue must also like running.
This is not a logical reasoning because the premises do not state that liking fishing and rock climbing implies liking running.
