An argument that since something is commonly supposed to be so, then it is so. Clearly invalid in general (e.g. it might commonly be supposed that the earth is flat, when it is not), but more compelling in special cases. For example if a society commonly supposes that a construction is grammatical, or that a term has a certain meaning, this may entail that the construction is grammatical, or that the word does have that meaning. The place of common consent, like common sense, in epistemology is not easy to establish. See also Herbert of Cherbury.
Philosophy dictionary. Academic. 2011.