I think it is both. We all have a personal style, unless we don't care about aesthetics at all or don't have the resources to invest in it. And of course it is shaped by what we see and the social implications of it.
I'm a bit of both (trend setter and follower). I pay attention to everything and take what I like, and make it my own.
Your style is a reflection of your personality, so it's "inborn" as much as your personality is. OTOH fashion sense is generally learnt, meaning you learn how to express your style in a way that's harmonious and nice to look at.
I think it is mostly learned, and I suspect mothers who are focused on it pass it down to children, and also children who obtain peer groups who are focused on it develop the skill.
There could be some innate tendencies that include a certain kind of social inclination (to either copy fashion to fit in or use it to stand out) and different kinds of awareness of the external world (colors, patterns), and other ways of relating to concrete ideas.
I have some awareness of clothes, but tend to use them as an understated metaphor for self-expression.
The first man to raise a fist is the man who's run out of ideas. H.G. WELLS
The first principle is that you must not fool yourself, and you are the easiest person to fool. FEYNMAN If this is monkey pee, you're on your own.SCULLY
I think you're born gravitating towards things as your personality develops. I have never, ever liked the color pink, even as a baby and toddler, but I did like the color black and I liked outrageous costume-y clothes. I've never grown out of those things.
Growing up, I definitely noticed what others were wearing.. In primary school we had uniforms, so I emulated what was best for matching my circle of friends, which happened to be boys.
In middle school I tried to develop my own style.. I liked Japanese things, renaissance clothing, wacky clothing, etc. so I worked as much as I could within school parameters with clothing in that fashion. I was a bit of a happy mess in middle school.
In high school, I had a whole other set of things to worry about. Boys were starting to hit on girls, people were wearing make-up and revealing clothing, and I just wasn't ready for all of it. I rebelled and went the entire opposite way--tomboy baggy clothing and the comfort zones I had in primary school. I still wanted to be in that boy-friend-zone, and I dressed my way there pretty effectively. It was less about what I wanted and more about surviving that war zone that high school tends to be.
Now-a-days, I still don't like pink, I still love costume clothing and renaissance attire, I still love Japanese inspired wear and I like the drab colors of an older army.. but now I know how to really marry those loves into things that look good on me and make sense. I can see fahionable blogs and tips on how to turn clothing into something else, and I can work with those frugal tips to create a good style based on what I love. I still have a boy-ish look to my daily wear clothing, but it's becoming more feminine overall as I am able to find garments that match what I want and need. I'm still frugal in nature, I don't just buy $200 skirts and shirts because they look good, my wardrobe still has items in it from elementary school (don't judge me :c ) so I don't often update it without a really good sale or a situation requiring a very particular garment arising.
Kantgirl: Just say "I'm feminine and I'll punch anyone who says otherwise!"
Halla74: Think your way through the world. Feel your way through life.
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I think there is a kind of base aesthetic people have. What that becomes and the extent to which the individual realizes it is up to them.
I, for instance, always had a sense of what did and didn't look good/fashionable. Up until recently, I never showed that through what I wore, but I could tell you that you should probably try the red shoes instead of the black for an element of interest.
While we're on subject, I notice that a lot of really well-dressed people don't necessarily have an actual sense of aesthetics and the components that go into a fashionable look. They just see what looks good or is popular and imitate it. It's only interesting because I feel like many get the sense that you have to be different, creative, or better to look like you just came out of the casual section of a JC Penney magazine. You really don't. Just look at what's in it and copy it. People won't know the difference and will think you're just as fashionable as every other trend-whore.
I think the interest is innate and leads to time researching etc which makes you better at it. And I think it could be considered an artistic talent as well, which tend to have a genetic base that is influenced by practice/experiences.
I'm neither a trend setter nor a trend follower in my group. More of a trend ignorer. I guess closer to a follower though, since I do occasionally get ideas from seeing other people wearing things. I'm far, far more interested in what looks "good" as opposed to what looks "fashionable", though.
edit: oh wow, yeah definitely peers would be the major source of learning for most people as opposed to direct research. I guess that didn't occur to me since I picked up zero from peers growing up
It depends on the mood of the day, I tend to wear stuff that's in, but if I'm a little too aware of some things, I look for other options that way I don't end up feeling ripped off if the styles aren't even close the next time that same season rolls around in case I don't have time or money to hit the mall before the season actually starts the following year, but there's stuff I pretty much always like in case some trend just plain doesn't appeal.