Argument from Parsimony

Concept and Historical Background

The Argument from Parsimony is a family of reasoning strategies that recommend simpler theories over more complex rivals, provided they explain the same phenomena equally well. It is closely related to, and often expressed through, Ockham’s Razor, typically summarized as “do not multiply entities beyond necessity.”

Ancient Greek philosophers, including Aristotle and the Stoics, employed simplicity considerations in theory choice, but the principle gained its most famous medieval formulation with William of Ockham (c. 1287–1347). Ockham himself used parsimony mainly in the context of metaphysics and theology, arguing, for example, against positing unnecessary universals or hidden metaphysical structures when more economical accounts of language and thought would suffice.

In modern philosophy and science, the Argument from Parsimony has become a key methodological and epistemic tool. It underlies common judgments that a theory is “overcomplicated,” “ad hoc,” or “metaphysically bloated,” and it plays a role in debates over scientific realism, the existence of abstract objects, and the evaluation of competing scientific theories.

Formulations and Uses in Philosophy

Philosophers distinguish several forms of parsimony:

• Ontological parsimony: Prefer theories that posit fewer kinds or numbers of entities (e.g., physicalism vs. dualism about mind).
• Ideational or theoretical parsimony: Prefer theories that use fewer basic principles, laws, or parameters (e.g., simpler dynamical laws in physics).
• Explanatory parsimony: Prefer explanations that do not introduce unnecessary causal steps or mechanisms.

The Argument from Parsimony can be framed as a norm of theory choice:

1. When two or more theories are empirically equivalent (fit all the same data),
2. And one theory is more parsimonious in relevant respects,
3. Then, ceteris paribus, we should prefer the more parsimonious theory.

In philosophy of religion, an argument from parsimony is sometimes invoked against theism: critics maintain that naturalistic accounts of the universe, consciousness, and morality posit fewer fundamental kinds of beings than theistic accounts that add a supernatural deity. Conversely, some theists argue that postulating a single divine cause is, in a different sense, more parsimonious than pluralistic or many-worlds explanations.

In metaphysics, parsimony is often central. For instance:

• Nominalists deploy it against realist theories of universals, arguing we should not posit abstract entities if we can explain predication in terms of language, resemblance, or sets of particulars.
• Eliminative materialists appeal to parsimony when questioning whether we need beliefs and desires as distinct entities over and above neurophysiological states.
• In debates about modality, some philosophers resist possible worlds as concrete or abstract entities, on the grounds that they are an ontological extravagance.

In philosophy of science, the Argument from Parsimony intersects with formal criteria like model selection (e.g., Akaike Information Criterion, Bayesian methods). These frameworks often treat simplicity as a proxy for avoiding overfitting: more complex models can fit existing data better but may generalize worse. Here, parsimony is not merely aesthetic; it is linked to predictive success and inductive reliability.

Criticisms and Limitations

The status of the Argument from Parsimony is controversial. Key questions include:

• Is parsimony a truth-conducive principle (tending to lead us to true theories)?
• Is it merely a pragmatic rule of thumb (for computational or practical convenience)?
• Or is it largely an aesthetic preference masquerading as an epistemic norm?

Critics raise several objections:

1. Underdetermination: Empirically equivalent theories may differ in countless ways. Simplicity might help choose among them, but there is no guarantee that the simpler theory is more likely to be true. Some argue that appealing to parsimony in such cases goes beyond the evidence.

2. Ambiguity of “simplicity”: Simplicity is multifaceted—ontological, syntactic, mathematical, explanatory—and these can come apart. A theory might be ontologically lean but mathematically complex, or vice versa. Critics contend that without a precise, non-arbitrary measure of simplicity, appeals to parsimony risk being subjective.

3. History of science: Some of the most successful theories (e.g., quantum mechanics, general relativity) are not “simple” in any naïve sense. Historical episodes suggest that the world can be irreducibly complex, and that more complex theories sometimes supersede simpler ones because they capture structure the simpler theories miss.

4. Circular justification: Attempts to justify parsimony often appeal to its past success in science, but such success is typically measured relative to theories already filtered by parsimony-based methods. This can render the argument circular or question-begging.

In response, defenders of the Argument from Parsimony offer several lines of support:

• Some Bayesian epistemologists argue that preferring simpler theories can be understood as assigning them higher prior probabilities, which can be rational if we treat complexity as statistically correlated with overfitting or with “gerrymandered” hypotheses.
• Others treat parsimony as a regulative ideal: even if not guaranteed to lead to truth, it structures inquiry by discouraging proliferating hypotheses beyond what the evidence demands.
• In philosophy of science, some suggest that simplicity is instrumental to explanatory depth, unification, and understanding, and that these cognitive virtues provide indirect epistemic support.

Overall, the Argument from Parsimony remains a widely used but philosophically debated tool. It shapes theory choice across metaphysics, epistemology, philosophy of science, and philosophy of religion, even as its ultimate justification and scope continue to be contested.