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.
BThe 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.
CAll 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°.
DMary 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.
