 It has been treated as an excuse in that, rather than acknowledge that the failure to reach agreement is due to such factors as imprecision, ignorance, or belligerence, instead theorists point to the terms and concepts under dispute and insist that they are always open to contest — that they are terms and concepts about which we can never expect to reach agreement.The disputes that attend an essentially contested concept are driven by substantive disagreements over a range of different, entirely reasonable (although perhaps mistaken) interpretations of a mutually-agreed-upon archetypical notion, such as the legal precept "treat like cases alike; and treat different cases differently", with "each party [continuing] to defend its case with what it claims to be convincing arguments, evidence and other forms of justification".Gallie speaks of how "This picture is painted in oils" can be successfully contested if the work is actually painted in tempera; while "This picture is a work of art" may meet strong opposition due to disputes over what "work of art" denotes.