“In deciding whether the conditions for variation exist, it is common ground that the change must be a material change of circumstances. This means a change, such that, if known at the time, would likely have resulted in different terms. The corollary to this is that if the matter which is relied on as constituting a change was known at the relevant time it cannot be relied on as the basis for variation. The controversial aspect of this appeal is whether it is also a pre-condition to variation that there be a change in the circumstances of the payor spouse and the child or children in whose favour the support provisions were made. In determining this issue it is important to bear in mind that an order for maintenance of children is made by assessing the needs of the children having regard to the means of the parents. The purpose of s. 17(4) appears to be to permit the court to vary the order when the relationship between those factors changes in a material way. There can be a material change in the relation of the factors if one of them undergoes a significant change because the relationship between them is altered. The following passage from the reasons for judgment of Keenan Dist. Ct. J. in Moosa v. Moosa (1990), 1990 CanLII 3966 (ON SC), 26 R.F.L. (3d) 107 (Ont. Dist. Ct.), at pp. 110‑11 is apt:
It is established beyond dispute that a dependent child is entitled to look to both parents for support. It is also established beyond dispute that each parent has an obligation to provide for the support of the child. The amount of the support to be provided is the amount that will meet the needs of that particular child. The measure of those needs depends on a number of factors including the age of the child and the standard at which that child could reasonably expect to be supported. The reasonableness of the expectation is to be measured against the means and circumstances of the parents who have the obligation to provide the support. I know of no reason why that expectation should be any different for a child who is the innocent victim of the breakdown of the relationship between its parents. If the ability of the parents or either of them increases or decreases, it is reasonable to expect that the level of support of the child will increase or decrease. [Emphasis added.]”