At what point does an action change from something you do sometimes to a habit? At what point does a habit become an addiction? Do those same points exist in reverse and are they in the same spot? Is this more of a medical question or maybe physiological? Is it a mental change you make (whether you know it or not) or a physical change? Why is it so hard to break but so easy to make worse?

Great set of questions. Certainly, these are matters that involve psychology and have an application in medicine, though philosophers from Ancient GreeK though onward have found it important to reflect on responsibility, habits, and determining when actions are truly voluntary. I suspect voluntariness is the key. The more we become habituated to a pattern of behavior, it seems that the more will power is required to break the pattern. I believe that Aristotle was right when he described the path to virtue in terms of habituation or the developing good habits or dispositions (to act justly, temperately, etc). In a sense, the virtuous person is someone who has developed a character so that they naturally and without struggle seek to do what is good. And the opposite would be true of a person in terms of vice; their character is such that they naturally and without struggle do what is cruel, destructive, and the like. Speaking more directly to your question(s) it seems that voluntary action is a scaler term (a matter of degree) and so would matters of habit or addiction. So, to take alcohol consumption, there seems to be a fairly common sense distinction between an occasional or "social" drinker, a habitual drinker, a heavy drinker, and an alcoholic, and these seem to map matters of voluntariness. Treatment centers and insurance companies are likely to treat the alcoholic as someone with very little, if any, voluntary control over their drinking, whereas someone who drinks habitually or regularly (say, one glass of wine a day) has more control, and the only occasional moderate drinker has even more control. For an excellent book on this later topic see Heavy Drinking by (and I am probably slightly misspelling his name) Finegrette.

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