This study shows the proper method for constructing a ground of appeal and cassation when violated by a court of first instance provision is article 6 of the Civil Code or article 233 § 1 of the Civil Procedure Code. The first of the mentioned provisions applies to apportioning the burden of proof between the parties to the proceedings. The second concerns the issue of free evaluation of evidence, which is clearly related to the stage of the judicial application of the law, and strictly speaking – the stage during which the authority evaluates the evidence. The purpose of this article is therefore to clarify the differences between the two legal bases and identify practical rules to assist the formulation of appeal and cassation grounds in this regard.