Anyone who opens a copy of Spinoza's Ethics will immediately be struck by its unusual layout, modelled on the classic geometry textbook: the Elementa geometrica of Euclid (ca. 300 B.C.E.). Starting from a few definitions and axioms, propositions are derived by means of deduction and this continues until the entire philosophical system, from its metaphysical foundations up to an elaborate theory of human bondage and liberation, has been unfolded. Rather than offering a discursive elaboration of the argument, Spinoza breaks it down to a sequence of definitions, axioms, propositions, and proofs. To this basic framework he adds a variety of elucidations in the shape of comments (scholia), prefaces, and appendices. Though all of these elements serve as links in the chain (and may therefore be invoked in the subsequent reasoning), the elucidations are written in a looser style. Here Spinoza occasionally steps aside in order to comment on his own argument. By furnishing these scholia himself, he departs from his model: explanatory comments were added to Euclid's textbook only in later ages. It is mainly as an oddity that the Euclidean layout of the Ethics has won historical fame. In view of the high esteem in which mathematics has generally been held, this is remarkable. Apparently philosophy, by the mere act of donning the classical costume of Euclidean geometrical discourse, does not acquire the incontrovertible and scientific aura of its mathematical model.