The Causative Nexus is an important part of the Diagnostic Step for Mental Capacity. In its simplest of forms, it can be described as the ‘link’ between the Functional Step of the two-stage test, and whether the Diagnosis is the origin for this outcome. Another way to consider the causative nexus, is as the ‘because’ or justification for why a diagnosis may be the causation for a person being unable to demonstrate decision making within the functional stage of the assessment.
Unfortunately, the Causative Nexus is often overlooked in everyday practice. This can be because the person conducting the assessment has not been effectively trained on how to complete and properly document the assessment.
At a recent Court of Protection User Group Meeting (July 2025) this topic was discussed in relation to Court of Protection Form 3 (COP3), and why some COP3 forms are rejected. The reply was as follows;
The issue is whether the COP3 submitted satisfies the decision-maker that there is a causative link [our emphasis] between functional incapacity and mental impairment/disturbance. Without commenting on any individual case, there are circumstances where evidence submitted makes it entirely appropriate for a decision maker to query this.
Court of Protection User Group Meeting (July 2025)
This reminds us just how important it is to understand exactly what the Causative Nexus is, and how it should be applied. Failure to properly understand the Nexus and how it applies could lead to flaws in the assessment; it may even lead to legal and regulatory ramifications further down the line.
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