What is the definition of influence and what is the effect of influence?

Armstrong J. went on to quote from Geffen v. Goodman Estate, 1991 CanLII 69 (SCC), [1991] 2 S.C.R. 353 at 377 and particularly the following: ...It seems to me rather that when one speaks of “influence” one is really referring to the ability of one person to dominate the will of another, whether through manipulation, coercion, or outright but subtle abuse of power. DISCUSSION

The propounder of the will has the onus, on a balance of probabilities to prove due execution of the will in accordance with the law, that the testatrix had knowledge and approved of the will and that the testatrix had testamentary capacity. The propounder is assisted in this burden by the rebuttable presumption that once the legal formalities of execution have been established, it is presumed that the testatrix knew and approved of the contents of the will and had the testamentary capacity to make a will. (Vout v. Hay et al., 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876).