The part that trips people up most is that capacity is not all-or-nothing. A person may be able to make some decisions but not others, and capacity can change over time. A capacity evaluation is an assessment of whether someone can understand information, appreciate consequences, communicate a choice, and reason well enough to make a specific decision, such as signing legal papers, managing money, consenting to medical care, or changing an estate plan.

These evaluations are often done by a physician, psychologist, psychiatrist, or other qualified clinician, sometimes with input from family members and records. There is no single nationwide test for every situation. The legal standard usually depends on the decision being made and the law of the state involved. In elder law, a capacity evaluation can shape whether a power of attorney, guardianship, or disputed will stands up when challenged.

In an injury claim, capacity can affect almost every step. A person who cannot understand a settlement may not be able to sign a binding release without help from a court-appointed representative, such as a guardian ad litem or curator under some state systems. Capacity findings may also affect testimony, medical decision-making, and claims of undue influence or financial exploitation. In short, the evaluation often determines who gets to decide, and whether that decision will hold.