Summary

G.E.M. Anscombe's "On Transubstantiation" defends the philosophical coherence of the Catholic doctrine of transubstantiation against common objections. The central thesis is that the substance-accident distinction, as understood in Aristotelian metaphysics, provides a logically sound basis for conceiving how the bread and wine can cease to be their former substances while their accidents (appearances) remain unchanged. Anscombe argues that criticisms often stem from a misunderstanding of these metaphysical concepts or an imposition of unsuitable philosophical frameworks.

The book clarifies the specific meaning of "substance" and "accident" within the Thomistic tradition, differentiating it from modern scientific or common-sense understandings. Readers gain a detailed philosophical defense of transubstantiation, understanding how it avoids logical contradiction by employing a specific metaphysical vocabulary and conceptual apparatus, and how specific objections are resolved within this framework.

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Key concepts

Substance — The underlying reality or essence of a thing, distinct from its observable properties.
Accident — A property or characteristic of a substance that can change without altering the substance's essential nature.
Per accidens change — A change in the accidents of a thing, not its substance.
Thomistic metaphysics — The philosophical system of Thomas Aquinas, particularly his concepts of substance and accident.