Card 2.6 · Root II — Epistemology
Rationality
Is it rational to believe what the evidence supports, or what serves you?
This node asks what makes a belief or an action rational, and whether the standard is one thing or several.
Where it sits
Under II. Epistemology. Borders 2.3, 3.2.4, 6.5.
The rival answers
| Position | Rationality is |
|---|---|
| Evidentialism | Proportioning belief to evidence, full stop |
| Instrumental rationality | Taking effective means to your ends, whatever they are |
| Bayesian rationality | Updating credences coherently as evidence arrives |
| Ecological rationality | Using heuristics well-fitted to the actual environment |
| Reasons-responsiveness | Being appropriately moved by the reasons there are |
Key figures
| Figure | Dates | Tradition | Contribution |
|---|---|---|---|
| Aristotle | 384–322 BCE | Greek | Practical wisdom as distinct from theoretical |
| David Hume | 1711–1776 | European modern | Reason as slave of the passions; it selects means, not ends |
| Max Weber | 1864–1920 | Sociology | Instrumental and value rationality distinguished |
| Herbert Simon | 1916–2001 | Analytic | Bounded rationality; satisficing rather than optimising |
| Gerd Gigerenzer | b. 1947 | Psychology | Heuristics as adaptive, not defective |
Connections
→ 2.3, 2.1 · ↔ 2.7.1, 3.2.4, 6.5, 2.8 · ◇ evidentialism, instrumental rationality, bounded rationality · ○ Axial Age; Early modern; Modern; Table 3
→ narrower questions · ↔ questions it borders · ◇ the positions, mapped in Part III of the book · ○ the eras and comparison tables (Parts IV and V)
The full card is in the book
In The Coordinates of Thought this card goes on to a worked example that sets the answers against one case, and to where the question touches daily life — page 118.
On Coordinates of Thought
Conversations about this question in Rationality & probability:
- Reading group: Clifford’s “The Ethics of Belief” and James’s “The Will to Believe” side by side 6 replies
- Hume was right: reason can choose the means, never the ends 6 replies
- The firing squad and my loan defaults: when does surviving need explaining? 5 replies
- Running a kitchen, I never pick the best option, just the first good one. Is that irrational? 5 replies
- Not every coherent prior is rational: subjective Bayesianism is far too permissive 5 replies
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