“At trial, the father sought to lead evidence about how the child support term in the Joint Agreement was negotiated, and what the parties intended. Although he gave evidence that was relevant to the interpretation of the terms of the agreement which was admitted for the purpose of explaining the surrounding circumstances to the agreement, his subjective evidence of the parties intentions in negotiations was contrary to the parol evidence rule and inadmissible for this purpose: Sattva at paras 59-61; 2356802 Ontario Corp. v. 285 Spadina SPV Inc., 2022 ONSC 7318 at para 53. The purpose of the parol evidence rule is to achieve finality and certainty in contractual obligations, and to hamper a party’s ability to use fabricated or unreliable evidence to attack a written contract: Sattva at para 59, citing United Brotherhood of Carpenters and Joiners of America, Local 579 v. Bradco Construction Ltd., 1993 CanLII 88 (SCC), [1993] 2 S.C.R. 316 at 341-42. Applying the parol evidence rule, the father’s evidence of the surrounding circumstances could not add to, subtract from, vary, or contradict the words of the written agreement: Ibid; 235 Ontario Corp. at para 53.”