E1P4D
Demonstration — Part I
Latin
Omnia quæ sunt vel in se vel in alio sunt (per axioma 1) hoc est (per definitiones 3 et 5) extra intellectum nihil datur præter substantias earumque affectiones. Nihil ergo extra intellectum datur per quod plures res distingui inter se possunt præter substantias sive quod idem est (per definitionem 4) earum attributa earumque affectiones. Q.E.D.
English (Elwes 1883)
Everything which exists, exists either in itself or in something else (Ax. i.),--that is (by Deff. iii. and v.), nothing is granted in addition to the understanding, except substance and its modifications. Nothing is, therefore, given besides the understanding, by which several things may be distinguished one from the other, except the substances, or, in other words (see Ax. iv.), their attributes and modifications. Q.E.D.
Modern English
Everything that exists, exists either in itself or in something else (E1A1). That is, outside the intellect nothing exists except substances and their affections (E1D3)(E1D5). So outside the intellect there is nothing by which several things could be distinguished from one another, except substances or, what is the same thing, their attributes and their affections (E1D4). Q.E.D.