<p>This paper proposes that Max Weber’s distinction between instrumental rationality (<i>Zweckrationalität</i>) and value rationality (<i>Wertrationalität</i>) in human action can be formally operationalised by applying quantum decision theory, and that this integration provides a probabilistic theory of integrity. Conventional management theory, grounded predominantly in instrumental rationality, provides an incomplete account of managerial action by neglecting value commitments that are irreducible to utilitarian calculation. The contemporary discourse on “value” in management—from value-based management and shareholder value to stakeholder values, the Triple Bottom Line of social and environmental value in addition to economic value, and the integration of ESG factors (environmental, social, and governance) into risk analysis and investment decision-making—remains fundamentally consequentialist, treating value as an outcome to be maximised without integrating ethical values and principles into the equation. This obscures Weber’s original distinction between instrumental rationality (calculating means to ends) and value rationality (acting from commitment to values “for their own sake,” independent of consequences). We argue that Weber’s two rationalities map onto the two complementary factors in quantum decision theory: the utility factor f(n) represents instrumental rationality, while the attraction factor q(n) represents value rationality. Integrity can thus be formally represented as P(n) = f(n) + q(n)—the integration of both forms of rationality into a probabilistic decision-making framework. This framework preserves the irreducibility of value rationality while demonstrating its systematic contribution to decision-making, particularly under moral uncertainty. It addresses calls in recent philosophy of management scholarship for integrating economic and deontic perspectives, providing the formal operationalisation that existing conceptual frameworks lack. We argue that this approach contributes to both the philosophy of management and business ethics by providing a formal account of how ethical values and principles function in decision-making without reducing them to instrumental considerations.</p>