The Limits of Thought: When Reasoning Requires Evidence to Decide

Reason can clarify concepts, expose contradictions, and derive consequences. These achievements do not necessarily establish which coherent explanation describes the actual world. This article examines the limits of reasoning in justifying claims about contingent reality. It proposes a principle of empirical discrimination: when competing explanations remain viable, further elaboration warrants a preference only insofar as it exposes a relevant inconsistency, changes the assessment of existing evidence, or supplies additional discriminating grounds. The principle is situated within work on underdetermination, likelihood, inference to the best explanation, and the distinction between pursuit and acceptance. Its distinctive contribution is an account of non-discriminating elaboration: five recurrent ways in which an explanation becomes richer without becoming better supported, each detectable through a symmetry test that asks whether the rival account could receive the same addition. Daniel Dennett’s report of a discussion with Ned Block about apparent blurriness during a visual laterality test provides the central case; a documented fingerprint misidentification provides a second. Dennett’s question, whether the blur explains the difficulty or the difficulty explains the blur, is extended to conviction itself: an explanation may seem well supported because it has become easy to think. The argument rejects a division in which thought generates possibilities and experiment mechanically selects truth. Reasoning can reveal unnoticed implications of existing evidence, while experiments depend on concepts, background assumptions, and interpretation. A diagnostic framework, applied in full to the central case, identifies when inquiry requires conceptual clarification, discriminating evidence, scrutiny of interpretation, or suspension of judgment.