How much in practice would someone minoring in a subject end up knowing about the subject as opposed to somebody majoring in it? How much extra work does it take to get a minor?
How much in practice would someone minoring in a subject end up knowing about the subject as opposed to somebody majoring in it?
Things vary of course. But a minor is maybe 5 classes whereas a major is 10+. So, about half as much. This can be useful if you only care about certain parts of a subject -- get a chemistry minor by taking physical chemistry + inorganic; you can skip organic and biochem.
It's also sometimes true that if you major in science and minor in certain humanities subjects (or vice versa), you can cover almost all of your gen eds this way. So some people can get a minor "for free" by choosing classes strategically.
As for how useful this is in practice: probably not much. It's a good way to document an interest; i.e., anyone can say "I'm interested in writing," but having a minor in writing shows that you mean it. And of course if your minor means you take more classes than you would have taken otherwise, then you'll know more stuff, and that is usually good at some level. But I suspect that few hiring or admissions decisions would have gone the other way but for the presence/absence of a minor.
There are at least two reasons to minor. One is to get some background in a field complementary to the major: say, chemistry for a biology major. Math and philosophy might actually go well together.
The second reason is just because you have an outside interest in something: literature for a biology major.
Some people get a minor because the required courses at a liberal arts college already contain most of it any way, so, why not. My philosophy minor was like that.
Some people take more than one minor. Actually double majoring is also possible many places.
The requirements for a minor might be approximately half of what they are for a major and might include a few upper level courses.
Some people just want a broad education. This has been true since the Renaissance, I'd guess.
Background on the US undergrad system.
A bachelors in the US is almost always four years, doable by a few in less and a few other students requiring more if they have difficulties.
Things are measured in "credit hours" and a credit is (most, not all places) about 15 hours of instruction, or an hour a week for fifteen weeks. Courses vary in how much they count, with three credits being typical but with variations in every program. Labs might require two hours per credit. Some courses are just one credit. There is no standard, but the above is common.
Students take about 15-16 credits per term for 8 terms (semesters), so the requirements for a degree are around 8*15 = 120 or so credits, maybe a bit more.
A major is usually a bit less than 60 credits and the rest of the courses/credits are general education requirements: history and such in a chem major.
So, it doesn't take "four years" for the major, but four years for the degree. But the prerequisite structure of the courses implies that the major courses are spread out with two or three taken per term.
A minor, on the other hand might be 30 or so credits, but the prerequisite structure spreads them out, but perhaps ten courses of 3 credits each taken over 8 terms, or 4 years. Some of the courses in a minor, indeed some in a major, might be required for a bachelor's in any case. So, science is required for many (most?) degree programs and so a chem major can do those in chemistry and get some of their "major courses" by taking the entry level science in chemistry.
Squeezing in two minors in addition to a major is a bit hard, as are double majors. It probably requires overloads and hard work. I once successfully completed 21 credits in a term where 15 was the norm. But I tried 20 in the following term and had to drop one as it was too intense and wound up with 17 that term.
Note that in both the major and in the gen ed requirements there is room for some choice of courses. They aren't rigidly prescribed. Some requirements are just to come up to the total successful credit hour requirement. So, using these options you can take courses in your minor or your major or (for some) whatever you like. There is a lot of flexibility. So, two student math majors might overlap in only the core required math courses and the core required gen ed courses, normally taken early on.
A few places like Dartmouth are on a quarter system with four quarters spread over the entire year. Most students there study for three of the four terms/quarters. The individual terms look different but the totals come out to be pretty equivalent. It is just in how you slice the apple. Since the summer quarter is just like the others, it makes better use of campus facilities overall. Faculty likewise normally teach in only some of the quarters, but when I was a visitor there (long ago) the standard was four courses per year.