E3P14D
Demonstration — Part III
Latin
Si corpus humanum a duobus corporibus simul affectum semel fuit, ubi mens postea eorum alterutrum imaginatur, statim et alterius recordabitur (per propositionem 18 partis II). At mentis imaginationes magis nostri corporis affectus quam corporum externorum naturam indicant (per corollarium II propositionis 16 partis II) : ergo si corpus et consequenter mens (vide definitionem 3 hujus) duobus affectibus semel affecta fuit, ubi postea eorum alterutro afficietur, afficietur etiam altero. Q.E.D.
English (Elwes 1883)
If the human body has once been affected by two bodies at once, whenever afterwards the mind conceives one of them, it will straightway remember the other also (II. xviii.). But the mind's conceptions indicate rather the emotions of our body than the nature of external bodies (II. xvi. Coroll. ii.); therefore, if the body, and consequently the mind (III. Def. iii.) has been once affected by two emotions at the same time, it will, whenever it is afterwards affected by one of the two, be also affected by the other.
Modern English
If the human body has once been affected by two bodies at the same time, whenever the mind afterward imagines one of them it will immediately recall the other as well (E2P18). But the mind's imaginings indicate the affections of our body rather than the nature of external bodies (E2P16C2). Therefore, if the body, and consequently the mind (E3D3), has once been affected by two affects at the same time, whenever it is afterward affected by one of them it will also be affected by the other. Q.E.D.