When you have a baby (or are about to have a baby and are reading up on babies), you start to see the word "colic" everywhere. It's rarely defined but always made out as something dreadful, or at least extremely unpleasant--and worse, it's portrayed as incurable and inescapable. Some babies are just "colicky" and nothing can be done about it.
This turns out to be not at all true. As far as I can tell from doing a whole lot of reading on the topic, there seem to be two kinds of colic: indigestion, and emotional meltdowns. Kit's had both, and we were able to identify them pretty quickly and treat them pretty straightforwardly. Kit is a very easy-going and good-natured kid, so that may be a factor, but hopefully this info will still be useful for other parents whose babies are not quite so chill.
1) Indigestion. "Our baby screams a lot and arches in pain when fed breast milk or standard formula," we said. "Well, some babies are colicky after feeding," our pediatrician said. Aha!, we thought. "Colicky" means "is upset about digestion pain". And indeed, when we stopped feeding Kit breast milk and regular formula and started using a super-digestible formula (from Honest Co., and we recommend it very highly--Kit spits it up even less than the supposedly ultra-gentle Similac Alimentum, and it's half the price), and made sure not to feed Kit more than their tiny stomach could hold, the colic went away. Kit still fusses a bit about 10 minutes after eating, and then farts a couple of times and settles right down. If we give a teaspoon or two of Colic-Ease every day, there's no fussing at all.
The pediatrician pointed out that since Kit wasn't vomiting up the meals, we could keep feeding breast milk (and the immunity benefits thereof) as long as we had a high tolerance for the screaming, until Kit got to be about three months old and the stomach developed enough to be able to digest the milk more easily. He did this in a very neutral way, which I appreciated--matter-of-fact, not pushing us one direction or the other. X and I stared at him with identical expressions of horror. It's not the screaming itself, but the idea of causing our child preventable pain, several times a day, for months. We considered dosing Kit with antacids, but our pediatrician shares our hesitation to put a very young baby on daily medication when there are non-medical options to pursue. So we switched to formula with some wistfulness but no regrets. That said, even if you're very dedicated to exclusively breastfeeding, there are ways of treating indigestion-type colic, and anyone (especially anyone not your doctor) who tells you that it's full-stop untreatable is probably wrong--any given attack of indigestion colic may just have to run its course, but a lot of those attacks can be prevented. Kit's always been an expert belcher and farter, so gas build-up isn't an issue, but if it were we could use simethicone drops and the Windi. Some babies have allergies to things the breastfeeding parent is eating, and a change in diet can help. There are lots of things to try.
2) Emotional meltdowns. T. Berry Brazelton defines this type of colic very clearly in his Touchpoints: Birth to Three, which is an excellent book that I think all new parents should keep on hand. Brazelton identifies it as coming from overstimulation during the day, which is why it reliably occurs in the evening. Since it doesn't have a physical cause, physical treatments (feeding, changing, gas drops, etc.) don't work, and soothing techniques like swaddling and pacifiers are of limited use. other_alice pointed me to a site about "the PURPLE crying period", which looks like much the same thing.
Brazelton advises making sure there are no physical problems to address and then leaving the baby alone in the crib to scream out their feelings, self-soothe, decompress, and sleep without further stimulation; in his experience, this can reduce the average duration of a colic attack by half. The "PURPLE crying period" site mentions a study in which babies cried less if their parents carried them around more often, as part of everyday life, rather than only picking them up when they were crying. So as with many things, the appropriate approach depends on you and your baby and your parenting style.
On Tuesday night, Kit had an emotional meltdown colic attack. It was pretty awful. But I realized that it reminded me of panic attacks, and then I knew what to do, because I have had many panic attacks and gotten pretty good at dealing with them. I held Kit gently and warmly, turned the lights down (installing dimmable LED bulbs and a dimmer switch in the baby's room is one of the best decisions I've ever made), rocked slowly in the rocking chair, and murmured quiet soothing things in a voice full of sympathy. I didn't try to offer a pacifier or stop Kit from screaming or thrashing, though I did loosely confine Kit's arms to keep either of us from getting punched in the face (and because Kit seems to find that sort of swaddling-by-hand very soothing, despite not liking actual swaddles). After a few minutes, the screaming and thrashing stopped and the baby fell asleep. Maybe ten minutes later, the cycle repeated once. And... that was that. All better. Pretty much the same thing happened when X was watching Kit Wednesday night while J and I were on our date night, and X did similar things and they were similarly effective. The key was that we both understood what it was like to feel overwhelmed and need to flail and yell, so we could stay calm and supportive while Kit vented. And we both know that while panic attacks feel like they're going to last forever, they do eventually end, and then everything is okay for at least a little while; so we could hold on to that knowledge instead of falling into our own panic and ending up trapped with the baby in a feedback loop of distress.
Apparently some colic attacks can last for hours. We're very lucky not to have seen that yet. At that point I probably would put the baby in the crib just to give myself a break from being up close with the screaming for all that time. But I'm hoping that gentle soothing and sincere sympathy will be enough to help Kit escape the multi-hour misery cycle.
Obviously this is all our personal experience; I'm not prescribing anything. Do what's best for you and your child. Just remember, this too shall pass--possibly with some gas. :)