Aquinas, Paley, and the Limits of Proof — McGrath (pp. 99–110)

Aquinas’s first way: motion/change (pp. 99–100)

Things change from potentiality to actuality; Aquinas argues that a series of movers requires a first unmoved mover. His argument concerns the grounding of change, not merely a physical event at the beginning of time.

First way and the Big Bang

A cosmic beginning can prompt questions about ultimate causation, but the Big Bang is not identical to Aquinas’s metaphysical first mover; a scientific beginning alone does not establish the whole theological conclusion.

Aquinas’s second way: efficient causation

Caused things cannot be their own efficient causes. Aquinas argues that an ordered causal series ultimately depends on a first efficient cause, called God.

Aquinas’s third way: contingency and necessity

Contingent beings can exist or fail to exist; Aquinas argues that the existence of contingent things ultimately depends on a necessary being.

Aquinas’s fourth way: degrees of perfection

Differences in degrees of goodness, truth, and nobility are used to reason toward a supreme source or standard of such perfections; this is not simply an opinion poll about human values.

Aquinas’s fifth way: teleology

Regular, goal-directed behavior in things lacking intelligence is taken to point toward an ordering intelligence. Teleology concerns directedness or purpose in natural processes.

Criticism: infinite regress

A critic may dispute whether an infinite explanatory series is impossible, or question why the proposed first cause is exempt from the causal requirement.

Criticism: identifying the first cause

Even if a first cause is established, further reasoning is required to show that it is the single God of Christian theism rather than another sort of source.

Criticism: divine continued existence

An argument for an originating cause does not by itself demonstrate that this cause still exists or remains involved with the universe.

Paley’s historical setting (pp. 104–105)

Newtonian mechanics, growing scientific understanding, and the Industrial Revolution made machines and their construction familiar comparisons for complex biological structures.

Paley’s mechanism and contrivance

A functional arrangement of parts appears to exhibit contrivance: the coordination of means to an end. Paley infers an intelligent designer from such organized complexity.

Watchmaker analogy

Finding a working watch suggests a maker because its parts cooperate to tell time; Paley extends this reasoning to living organisms.

Eye and telescope

Paley compares the human eye with an optical instrument, arguing that the eye’s elaborate arrangement for vision displays at least as much apparent design as a human-made telescope.

Hume’s objections

An analogy with human artifacts might suggest multiple designers rather than one; it cannot establish the designer’s moral goodness or that the designer continues to exist.

Paley’s response

Paley appeals to recurring patterns of design, consistent natural laws, and the integrated effectiveness of natural contrivances. These features are intended to strengthen the inference to a coherent designer.

Paley and Darwin

Paley largely treats biological structures as fixed products of design. Darwinian evolution explains adaptation through descent with modification and natural selection, challenging the need for separate direct design of each feature.

Dawkins and Plantinga

Dawkins argues that cumulative natural selection can produce apparent design without foresight. Plantinga holds that evolution as a biological mechanism need not exclude divine guidance or providence.

Kalam argument (p. 102)

Whatever begins to exist has a cause; the universe began to exist; therefore the universe has a cause. Whether the premises hold and what sort of cause follows remain debated.

What counts as proof? (pp. 108–110)

Mathematical and logical proof derives conclusions from premises through valid deduction. Scientific justification usually assesses explanatory adequacy, observations, and competing models rather than achieving deductive certainty.

Cosmology and quantum theory as examples

Competing cosmological accounts and interpretations of quantum theory show that evidence can underdetermine a unique theoretical interpretation. Theological arguments also require scrutiny of premises and inference.