Underdetermination of Theory by Evidence
Available evidence may be compatible with more than one explanatory theory.
The Mechanism: Underdetermination occurs when the available evidence does not uniquely select one theory from multiple alternatives. Pierre Duhem and later philosophers of science explored how hypotheses are tested alongside auxiliary assumptions.
The Philosophical Pivot: An experiment rarely tests a claim in isolation. Instruments, background theories, and assumptions about measurement help connect a prediction to an observation.
The Horizon: Researchers compare theories using new predictions, simplicity, explanatory scope, and coherence with established knowledge. These criteria guide judgment but may not produce a single answer immediately.
Underdetermination does not mean all theories are equally credible. Some alternatives make failed predictions, require ad hoc assumptions, or lack explanatory power.
Scientific communities can reduce uncertainty by developing new instruments and seeking evidence that makes competing theories diverge.
The existence of alternatives is a reason for careful testing, not a reason to abandon the distinction between better and worse explanations.
Evidence can constrain explanation without always choosing only one explanation at once.
What new observation would make the competing explanations I accept stop looking equally plausible?