To be called a passion an activity should meet at least two of these requirements:
1) that you pursue it for years with keen interest and not out of a compulsion, necessity, or others' expectations
2) where you discover and explore new boundaries
3) that it puts you in ‘flow’ so that you merge with the action that you do
Additionally, it should satisfy one further criterion:
4) that you show a conscious striving for improvement that goes well beyond the casual wish to improve, including doing the unpleasant things and the hard slog that goes with a serious desire to improve.
I think that one's relationship with one's partner, or one's children, and sexual passion itself, should be excluded, as being different in kind.
One of the interesting aspects of writing about this topic is that there is an 'objective' and a 'subjective' dimension. Thus I can judge what my passions are according to the above criteria, but this may not tally with what I internally feel to be my passions. There is an element to the topic that resists being pinned down. It's as though a passion is an interest with some added mysterious element that quickens the pulse (or maybe slows it down!) This should not be surprising, given that the notion of passion derives its origin from sexuality, an area that is notoriously difficult to analyse. I think it's a good idea to keep the analogy with sexual passion in mind when discussing the topic of non-sexual passions. A somewhat different use of the word is seen in the passion of Christ.
I think that loving what you do is a major factor in passion, though it may not need to be one of the explicit criteria. Certainly, a passion connects with your heart. It is not a matter of it filling time but of your stealing time for it. It makes you come alive. You wake up thinking about your passion and look forward to doing it. Enthusiasm is the key word.
I think the determination of what is a passion cannot be objective, as the internal component - in short, how much the activity touches your heart - cannot be evaluated very well by anyone else. Discussing passions reminds me of discussing creativity. People tend to put creativity on too high a pedestal, whereas with passion they tend to set the bar too low, in order not to go down as being passionless. It is more socially acceptable to be uncreative than unfeeling.
I think that the only serious candidates for passions in my own case are photography, fractals, writing, squash, climbing and trekking. Only squash, climbing and trekking put me in flow, though I may get momentary flow in some of the others. Anything that uses the brain throws me into anxiety or thinking too much!
Photography: 1, 2, 4
Fractals: 1, 2, 4
Writing: 1, 2, 4
Squash: 1, 3, 4
Climbing and trekking: 1, 2, 3, 4
My PC: 1, 2, 3, 4
I was reluctant to add my PC to the list, but I spend most of my free time at the keyboard, and the PC, though only a tool, organises or enables so many of my activities, including photography, fractals, and writing. There certainly is an element of addiction, as well. The PC is also my connection with the world, through email and the Net.
I have loved music all my life, it certainly puts me in flow and I have transcended boundaries by learning to appreciate new or difficult music. Yet I don't think my interest is serious enough to qualify as a passion. Only 1, 2, 3.
I am spending a lot of time and thought on chess at the moment, but I would hesitate to call it a passion because I am not putting in enough serious study of chess. Even though I analyse games I lose, have ordered a book on chess, am learning an opening, and think a lot about my next move in the games I am playing, I still don't think I am serious enough about it. I think the "extra mile" criterion is a valid cut-off point to distinguish an interest from a passion. I ask myself, "Am I doing everything I can to improve?" Of course, unless you are Andre Agassi, you can always do more, but there should be some way of framing the criterion so that it reliably separates interests from passions. Only 1 & 2
My interest in reading is haphazard. I greatly value some books and see them as an invaluable window on the world, but my involvement in reading is far too patchy, and too occasional to come close to being a passion. Only 2 & 3.
Mosaics are an abiding interest that occasionally consumes a lot of time and effort, but my pursuit of this activity has been too patchy over the years to qualify as a passion. Only 1 & 2.
My interest in travel has cooled somewhat, though I am still quite keen to do it. I am a little jaded, especially about seeing yet another city. Travel to natural locations is another matter, but that comes under trekking and climbing. Only 1 & 2.
Evaluating the above and other candidates, I find there are quite a few that meet #1 but not many that meet #4. For me, the fourth criterion seems to be the key one, but maybe I am too demanding? There are many activities that I have pursued over the years (soccer, puzzles, glass work, films etc) and they have occasionally put me in flow and breached boundaries, but in all cases stop short of the "extra mile" requirement.
How is an addiction different from a passion? In other words, how do you distinguish between doing something out of a compulsion and doing it out of love? Some activities may have both addictive and passionate components. For that matter, how do you avoid being addicted to your passion, assuming you are fortunate enough to have one?
I suspect that all genuine passions do have an element of addiction in them. It is hard to define addiction properly. One obvious difference is that an addiction has a negative impact on an individual's life, but one can also talk about positive addictions, such as to being on time at the office, or to writing emails without grammatical or spelling errors.
Wikipedia says: "Addiction can be viewed as a continued involvement with a substance or activity despite the negative consequences associated with it." However, this definition excludes positive and neutral behaviours. Here is my attempt at a definition: an addiction is a persistent emotionally-driven behaviour to which the person gives too much value. Of course, the problem is how to define "too much value"! It's a bit like trying to define the difference between pornography and erotica, cf "What turns you on is porn, what turns me on is erotica".
Then there is obsession, which is an extreme preoccupation with something. This too, should be distinguished from passion.