Definition of "Reason" :

noun: the capacity for rational thought or inference or discrimination

"We are told that man is endowed with reason and capable of distinguishing good from evil."

noun: a fact that logically justifies some premise or conclusion

"There is reason to believe he is lying."

noun: an explanation of the cause of some phenomenon

"The reason a steady state was never reached was that the back pressure built up too slowly."

noun: a justification for something existing or happening

"They had good reason to rejoice."

noun: a rational motive for a belief or action

"The reason that war was declared."

noun: the state of having good sense and sound judgment

"He had to rely less on reason than on rousing their emotions."

verb: think logically

"The children must learn to reason."

verb: decide by reasoning; draw or come to a conclusion

"We reasoned that it was cheaper to rent than to buy a house."

verb: present reasons and arguments