Structural Rationality

Concept and Motivation

Structural rationality is a way of understanding rationality that focuses on the relations among an agent’s mental states—their beliefs, intentions, preferences, and other attitudes—rather than on how well those states correspond to the external world. An agent is structurally rational, on this view, when their attitudes form a coherent, well‑organized structure that satisfies certain formal or logical constraints.

This approach is motivated by the idea that there is an important difference between:

• whether it is reasonable to hold a particular belief or intention given what else one thinks and intends, and
• whether that belief or intention is correct, successful, or truth‑tracking.

Structural theorists argue that both dimensions matter, and that philosophy should carefully distinguish structural assessments (about coherence) from substantive assessments (about truth, evidence, or value).

Structural vs Substantive Rationality

The contrast between structural and substantive (sometimes called “responding‑to‑reasons” or “fittingness”) rationality is central.

Structural rationality evaluates:

• how well attitudes fit together,
• whether they follow patterns akin to consistency, transitivity, or means–end coherence, and
• whether they respect formal norms such as logical closure or the axioms of decision theory.

By contrast, substantive rationality evaluates:

• whether an agent’s beliefs are supported by the evidence,
• whether preferences and choices are reasonable given the actual stakes and values, and
• whether the agent responds correctly to normative reasons that in fact apply.

For example, an agent who believes that the lottery is fair and that it has astronomically low odds, but also believes that buying a ticket is very likely to make them rich, may be structurally irrational because their beliefs are mutually inconsistent. Even if, by chance, they win the lottery, structural accounts say the original set of attitudes was irrational due to its internal incoherence. Substantive accounts instead focus on whether it was reasonable, evidence‑wise, to expect to win.

Some philosophers hold hybrid views, according to which rationality has both structural and substantive aspects. Others propose that only one of these captures what is fundamentally at stake in assessments of rationality, treating the other as derivative or as a different kind of normativity (for instance, epistemic or moral rather than strictly rational).

Examples and Debates

A standard way to illustrate structural rationality is via coherence requirements, such as:

• Belief consistency: Do not believe both p and not‑p.
• Enkratic coherence: If you believe that you ought to do A, then intend to do A (barring strong excusing conditions).
• Means–end coherence: If you intend an end E and believe that doing M is a necessary means to E, then (absent alternatives) intend M.

These norms do not directly say what to believe or intend; they instead regulate how different attitudes must stand to one another. An agent could satisfy these norms while having wildly false beliefs, or could violate them even while many of their individual beliefs are true.

Several controversies surround structural rationality:

1. The nature of the “requirements.”
   Some theorists describe structural rationality in terms of requirement relations among attitudes (“If you believe that you ought to do A, you are rationally required to intend A”). Others doubt that such requirements are best understood as strict rules, instead viewing them as patterns of defeasible guidance, virtues of coherence, or even as constitutive features of agency.

2. Wide‑ vs narrow‑scope norms.
   A technical debate concerns whether structural requirements have a wide scope (governing the entire conditional attitude set) or narrow scope (governing only one of the attitudes). Wide‑scope formulations avoid telling agents which specific attitude to change; they simply forbid certain combinations. Narrow‑scope formulations instead can say, for example: “If you believe you ought to do A, you must intend A.” This connects structural rationality to broader questions about logical and practical inference.

3. Explanatory role.
   Proponents argue that structural rationality plays a key role in explaining:

   • why incoherent agents appear confused or self‑undermining,
   • how we diagnose irrationality in others even when we lack full information about their evidence, and
   • why norms of logic and decision theory seem to have a special authority in governing thought.

   Critics contend that these explanatory roles can be filled by substantive rationality alone, or by appealing to other normative domains (such as morality, prudence, or epistemic justification), without positing a distinct structural dimension.

4. Normativity and criticism.
   A further debate asks in what sense structural rationality is genuinely normative. If an agent’s attitudes are structurally incoherent but substantively well‑supported by evidence and reasons, are they genuinely criticizable? Some argue that coherence has intrinsic normative force; others suggest that structural norms matter mainly because they tend to promote success in truth‑seeking or decision‑making, thus deriving their importance from substantive goals.

In contemporary philosophy of mind, action, and epistemology, structural rationality functions as a key tool for analyzing agency, deliberation, and mental architecture. It provides a framework for understanding how attitudes must be organized for an agent to count as thinking and acting in a distinctively rational way, even before one asks whether the agent’s views are true or their choices wise.