With the rise of Stoicism as the most influential dogmatic philosophy of the Hellenistic era, the problem of fate versus free will came to the fore, and Antiochus responded by rejecting fate ( heimarmenê ) as an efficient cause, relegating it to the class of "material cause" ( aition prokatarktikon ), along with time, matter, and other things that are necessary, but not sufficient, to produce an effect. This allowed for efficient causes to arise from human initiative, and preserved the freedom of human activity, or at least response, within an ordered cosmos.
Here therefore we may divide all the perceptions of the mind into two classes or species, which are distinguished by their different degrees of force and vivacity. The less forcible and lively are commonly denominated Thoughts or Ideas . The other species want a name in our language, and in most others; I suppose, because it was not requisite for any, but philosophical purposes, to rank them under a general term or appellation. Let us, therefore, use a little freedom, and call them Impressions; employing that word in a sense somewhat different from the usual. By the term impression , then, I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will. And impressions are distinguished from ideas, which are the less lively perceptions, of which we are conscious, when we reflect on any of those sensations or movements above mentioned.