This is a great post full of helpful information from Facebook from M.K., in response to a post reading: "What do you think about this?? The debate of whether Epicureans were atheists or not. The argument is that they just use the logic they created about the gods so that it didn't contradict their beliefs and that they could still believe in them so that they didn't get prosecuted for being nonbelievers. What are you're thoughts on that? I read this debate going both ways but wanted to know what other fellow Epicureans think."
There is no debate. They not only did not believe in no god, they believed in poly (many) theoi (gods).
Extant Epicurean texts demonstrate they dislike being called atheists.
Diogenes of Oenoanda [Fr. 16] denies with disgust the charge that they believed there were no gods. An abhorrent view he attributes to Diagoras of Melos (apparently an ancient Richard Dawkins) and another toned down version to Protagoras of Abdera (one of my favourite advocates of classics education today describes herself as a Protagorean agnostic). He avows Epicureans are properly the "most pious people."
Philodemus' fragments from Herculaneum, Lucretius, the Epicurean exposition put in the mouth of a one Gaius Velleius by Tully in De Natura Deorum.
All are very clear a vibrant and live conviction in that there are gods was a pillar of Epicureanism.
Cicero actually insinuates they seemed to have an improbably expert knowledge of what the gods look like and how they live [Tum Velleius fidenter sane, ut solent isti, nihil tam verens, quam ne dubitare aliqua de re videretur, tamquam modo ex deorum concilio et ex Epicuri intermundiis descendisset]. Epicurean pronouncements on the gods were more self-assured than most of the other schools.
The gods are integral to Epicurean ethics as a standard to aspire to of absolute ataraxia. And are central to the anthropological aetiology of the school. Human beings are erect, sentient, some times sapient, with eyes aimed above: because they are like the gods.
Epicurus' argument for the existence of gods is actually attractive and rather logically durable. Certainly defensible.
Since the senses are the sources of all knowledge, even of dreams, and human beings have a fairly universal acquaintance with gods - that knowledge must come from something materially real.
Knowledge of gods is a πρόληψιν - a mental preconception imprinted indelibly on the human mind.
This is even in the letter to Menoeceos, where Epicurus says a knowledge of the gods is engraved on our minds and so we know they exist "since knowledge of them is by clear vision derived from sensation." [ἐναργὴς γὰρ αὐτῶν ἐστιν ἡ γνῶσις’]
Lucretius suggestively seems - or at least could be read to - to nod toward a time when people saw gods but now don't (save in sleep). The prolepsis peoples still persistently have of them derives somehow from that dim distant past.
To call all of this "functional atheism," is to too easily abandon the field to the Abrahamic tradition. Gods do not need to be tirelessly provident and maniacally judgemental to exist.
In the classical world, that (Abrahamic) kind of thinking was considered populist (plebish). Crucially important to the average every-person without the time, inclination or education to think hard about these things and be good without an all-seeing eye anxious to punish. It had a name: superstition.
It was that which was the polar extreme of atheism, not belief in gods.