Mont. Code Ann. § 25-9-714
25-9-714 Supplementary general principles of law
25-9-714 . Supplementary general principles of law. Unless displaced by particular provisions of this part, the principles of law and equity, including the law merchant, and the law relative to capacity to contract, principal and agent, estoppel, fraud, misrepresentation, duress, coercion, mistake, bankruptcy, or other validating or invalidating causes supplement its provisions.