reason in WordNet English dictionary

1. present reasons and arguments
   argue  reason 
   
2. decide by reasoning; draw or come to a conclusion
   "We reasoned that it was cheaper to rent than to buy a house"
   reason  reason out  conclude 
   
3. think logically
   "The children must learn to reason"
   reason 
   

1. a justification for something existing or happening
   "he had no cause to complain"; "they had good reason to rejoice"
   cause  reason  grounds 
   
2. a rational motive for a belief or action
   "the reason that war was declared"; "the grounds for their declaration"
   reason  ground 
   
3. 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"
   reason  understanding  intellect 
   
4. 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"
   rationality  reason  reasonableness 
   
5. a fact that logically justifies some premise or conclusion
   "there is reason to believe he is lying"
   reason 
   
6. 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"
   reason