cre·du·li·ty /krɪˈduləti, ˈdju-/
  易信,輕信
  Cre·du·li·ty n.  Readiness of belief; a disposition to believe on slight evidence.
     That implict credulity is the mark of a feeble mind will not be disputed.   --Sir W. Hamilton.
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  credulity
       n : tendency to believe readily