Id omne quod ad lætitiam conducere imaginamur, conamur promovere ut fiat; quod vero eidem repugnare sive ad tristitiam conducere imaginamur, amovere vel destruere conamur.
English (Elwes 1883)
We endeavour to bring about whatsoever we conceive to conduce to pleasure; but we endeavour to remove or destroy whatsoever we conceive to be truly repugnant thereto, or to conduce to pain.
Modern English
We strive to bring about everything we imagine conduces to joy. Whatever we imagine to oppose joy, or to conduce to sadness, we strive to remove or destroy.