Definition of reason verb from the Oxford Advanced Learner's Dictionary

     

    reason

     verb
    verb
    BrE BrE//ˈriːzn//
     
    ; NAmE NAmE//ˈriːzn//
     
    Verb Forms present simple I / you / we / they reason
    BrE BrE//ˈriːzn//
     
    ; NAmE NAmE//ˈriːzn//
     
    he / she / it reasons
    BrE BrE//ˈriːznz//
     
    ; NAmE NAmE//ˈriːznz//
     
    past simple reasoned
    BrE BrE//ˈriːznd//
     
    ; NAmE NAmE//ˈriːznd//
     
    past participle reasoned
    BrE BrE//ˈriːznd//
     
    ; NAmE NAmE//ˈriːznd//
     
    -ing form reasoning
    BrE BrE//ˈriːznɪŋ//
     
    ; NAmE NAmE//ˈriːznɪŋ//
     
     
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  1. 1[transitive, intransitive] reason (that…) | + speech to form a judgement about a situation by considering the facts and using your power to think in a logical way She reasoned that she must have left her bag on the train. They couldn't fire him, he reasoned. He was the only one who knew how the system worked. They reasoned, correctly, that the enemy would not attempt an attack at night.
  2. 2[intransitive] to use your power to think and understand the human ability to reason
  3. Word Origin Middle English: from Old French reisun (noun), raisoner (verb), from a variant of Latin ratio(n-), from the verb reri ‘consider’. Phrasal Verbsreason something outreason with somebody
See the Oxford Advanced American Dictionary entry: reason