Sextus Empiricus Pyrrhoniae Hypotyposes 3.4.15

[15] The majority of them hold that of these Causes some are immediate, ¹ some associate, some co- operant; and that causes are ‟immediate” when their presence involves the presence, and their removal the removal, and their decrease the decrease, of the effect (it is thus, they say, that the fixing on of the halter causes the strangling); and that an ‟associate” cause is one which contributes a force equal to that of its fellow-cause towards the production of the effect (it is thus, they say, that each of the oxen which draw the plough is a cause of the drawing of the plough); and that a ‟co-operant” cause is one which contributes a slight force towards the easy production of the effect, as in the case when two men are lifting a heavy load with difficulty the assistance of a third helps to lighten it.