The Principles advocate a radical new approach to determining parenting arrangements after separation. The central concept is found in Section 2.08: “(T)he court should allocate custodial responsibility so that the proportion of custodial time the child spends with each parent approximates the proportion of time each parent spent performing caretaking functions for the child prior to the parents' separation.” This is the “past caretaking” standard. It should be seen as a ‘standard,’ rather than a rule, since the ‘rule’ can be modified on many different grounds. The past caretaking standard is based on the concept of continuity between the intact and separated family.

The presumptive allocation of custodial responsibility that results from this assessment can be modified, but only to the extent necessary to achieve other objectives contained in Section 2.08(1). There are eight objectives in Section 2.08 and a number of exceptions provided in Section 2.11. This latter sets out a number of justifications for limiting the parental responsibility of a parent in order to protect the child, the other parent, or other member of the child's household from harm, including abuse, neglect, or abandonment of a child, domestic violence, and abuse of drugs or alcohol. Given the overlap between Sections 2.08 and 2.11, some factual circumstances may be argued on more than one ground.

The past caretaking approach is also relevant to the allocation of responsibility for making significant parental decisions.