And as Cassius Amicus wrote somewhere too : Just don't get confused and think that this description implies some different type of pleasure than what you already understand the word to mean. The word "pleasure" includes every possible type of mental and physical sensation you find pleasurable, from sex to fine art to fine music to whatever. There are no "good" and "bad" pleasures - pleasure is a faculty which tells you what is pleasing - nothing more, nothing less - and it's up to you to weigh and judge the consequences and decide which pleasures to pursue.
All this is why Cicero summarized the Epicurean position as "a life of tranquility crammed full of pleasures" in his Defense of Publius Sestius 10.23 ("“…Nothing is preferable to a life of tranquility crammed full of pleasures.”)
However, if you check in at the philosophy department of most any college or philosophy group on the internet, and say "Ataraxia, a state of mental tranquility free from disturbance, is the ultimate pleasure and maintaining it is how Epicureanism is applied" you will get an A+
You just have to decide whether your goal is pleasing the philosophy professors, or having a realistic understanding of what Epicurus said about how to live.
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It's not just the technical use of the word ataraxia that I want to warn about but the combination with the following sentence that implies that all that is necessary to get to this ultimate state is to *subtract* something:
"Ataraxia, a state of mental tranquility free from disturbance, is the ultimate pleasure and maintaining it is how Epicureanism is applied. This means eliminating superstitious views that cause fear or disturbance and accepting your own mortality."
Again, yes it is absolutely true that we must eliminate superstition (PD1) and eliminate fear of death (PD2). Those are the two biggest false opinions we confront so that is why they are highlighted.
But there is a THIRD false opinion - and that is that there is some goal in life higher or better or to be preferred over pleasure. God and Death aren't the only demons to swat, you also have to swat the demons that there are absolute guides to life such as virtue or "being a good person" or "following god" that everyone must follow. That's where PD3 and PD4 come in, but they are written in a technical way that makes them well-suited for debating Plato, but poorly suited for new students of the philosophy.
Every animal at birth, including humans before they are corrupted by "virtue" or "religion", knows that nature calls them to pursue the various mental and physical pleasures of life. That is a premise of the entire conversation, so you don't get to the best life just looking for demons to swat and subtracting them from life. if you sit in your garden and close off your life with no contact with any ordinary pleasures of mind and body, you have NOT reached the best life. You get to the best life by finding and pursuing those pleasures that matter to you, even if that means accepting some pain as the price. You fill your life with pleasures, make sure you've eliminated the two biggest pains (fear of god and fear of death) and then you are well on your way. Depending on your other circumstances unique to you, your life is both peaceful (free of the worst fears/pains) and crammed full of pleasures.