Where the physical custody of minor children is in dispute between either divorcing parties or in a situation of unwed parents, the trial Court must find what would be in the child's best interests in determining which parent should maintain physical custody. This standard of proof is gender neutral under New Hampshire law and evidence may be presented by either parent to suggest why the child should be primarily in one parent's custody or the other. The judge or marital master would employ a preponderance of the evidence standard which would govern the final decision of the Court. This standard provides that if one parent and situation is more suitable by a reasonable probability of the evidence, that physical custody should be awarded to that parent.

Once an initial custody decision has been entered by the trial Court, it becomes much more difficult to modify custody in future years. In effect, once custody is established with one parent, the other parent attempting to change the custodial arrangement has a much more difficult case and a higher burden to convince the Court that a change should occur. The underlying basis for this concept is the Court's recognition of a child's psychological need for continuity and stability in family relationships. If parents were able to petition the Court regularly for a change in custody upon less than significant evidence, the risk that a child would bounce from one home to the other is a likely possibility. This "standard" of review was established in the case of Perrault v. Cook, 114 N.H. 440 (1974). In Perrault, the Court ennunciated the standard as follows:

The effect of the Perrault case has been to discourage modification of custody except in situations where a substantial harm is present. The Perrault case and similar standards in other jurisdictions throughout the country were largely established at a time when the norm in a custody case involved an award of primary physical custody to one party with a traditional visitation schedule to the non-custodial parent which consisted of weekends and other times throughout the year. In such a traditional Court order and family dynamic, it was clear to Courts and mental health professionals that the substantial harm test of Perrault was the appropriate standard.

With changing developments in the area of child custody in the past twenty-five (25) years, there has been an expansion of situations where parents are sharing physical custody as never before. Joint physical custody arrangements can run the gamut from sharing the children on alternating weeks, sharing the children during the school year and summers, or having other schedules where each parent spends substantial time with the children throughout the year. In those circumstances when one parent or the other seeks to modify the custodial arrangement to a sole physical custody award, the question of what standard to employ has often perplexed attorneys, marital masters and judges. Some family law practitioners and even judges in New Hampshire were convinced that in any modification even where joint custody was involved, the Perrault standard was the proper test. Others felt that the best interests of the child should control and, as a consequence, a modification from joint physical to sole custody would be easier to accomplish. What is clear is that prior to a recent New Hampshire Supreme Court case, the appropriate standard of proof was subject to different interpretations.

In a decision of the New Hampshire Supreme Court dated July 23, 2001, in the case of Pasquale v. Paulson, the court found that in circumstances where joint physical custody is no longer workable, the Perrault standard does not apply. Rather, the master or judge should use the best interests of the child standard to determine which parent should be awarded physical custody. In the Pasquale case, the Court has placed the judge in essentially the same position as if making an initial custody award where the Court must consider the relative abilities of both parents to promote the welfare of the child, and where the Court must choose differing factual assessments and determine what would be in the child's best interests.

This new decision of the New Hampshire Supreme Court clarifies considerably the law in New Hampshire when it comes to a modification of joint physical custody. The Court also reiterated and reaffirmed the prior case law in New Hampshire that provides where a modification of legal custody is concerned, that the best interests of the child standard is applicable.