Noun

• S: (n) reason, ground (a rational motive for a belief or action) "the reason that war was declared"; "the grounds for their declaration"
• S: (n) reason (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"
• S: (n) reason, understanding, intellect (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"
• S: (n) rationality, reason, reasonableness (the state of having good sense and sound judgment) "his rationality may have been impaired"; "he had to rely less on reason than on rousing their emotions"
• S: (n) cause, reason, grounds (a justification for something existing or happening) "he had no cause to complain"; "they had good reason to rejoice"
• S: (n) reason (a fact that logically justifies some premise or conclusion) "there is reason to believe he is lying"

Verb

• S: (v) reason, reason out, conclude (decide by reasoning; draw or come to a conclusion) "We reasoned that it was cheaper to rent than to buy a house"
• S: (v) argue, reason (present reasons and arguments)
• S: (v) reason (think logically) "The children must learn to reason"