According to Kohlberg's theory, what level of morality is it, when morality…

Concept: Kohlberg's theory of moral development groups moral reasoning into three levels, distinguished by the source of the moral standard a person uses: an external consequence, a social convention, or a self-chosen ethical principle. At the Pre-conventional level, morality is judged by direct consequences to oneself, such as avoiding punishment or seeking reward. At the Conventional level, morality is judged by conformity to social rules, laws, and the expectations of others, so as to maintain approval and social order. At the Post-conventional level, morality is judged by abstract, self-accepted ethical principles, such as justice, rights, and human dignity, that a person has internalised and will follow even when they conflict with law or social convention.

Application: The question describes a morality whose standard is self-accepted moral principles, meaning principles the person has internalised and adopted as their own rather than an external punishment or an external social rule. That description matches exactly the defining feature of the Post-conventional level of Kohlberg's theory.

Cross-check: Checking each level against the stem's criterion, a standard built on self-accepted principles, confirms the choice and rules out the others:

• Pre-conventional anchors morality to consequences to oneself, such as punishment avoidance or reward-seeking, not to self-accepted principles.

• Conventional anchors morality to conformity with social norms, authority, and law, that is, approval from others, not principles the person has chosen for themself.

• Post-conventional anchors morality to self-accepted, internalised ethical principles that can hold even against law or convention, precisely the standard described in the stem.

Result: A morality standard built on self-accepted moral principles is the Post-conventional level.