Back when I was a research scientist, I straddled the boundary between “hard” and “soft” sciences. I did social psychology, which is a pretty soft science as sciences go, but I paired it with biology and physiology in general and endocrinology in particular, which meant getting a taste for some of the harder stuff.
I have never particularly liked the terms “hard” and “soft”, though, because it’s too easy to conflate them with “hard” and “easy”. There’s a saying that goes: the soft sciences are easy to do poorly and hard to do well. They are easier to do poorly than the hard sciences, and harder to do well than the hard sciences. Here, have a chart:
What’s going on here? The hard sciences are better developed than the soft sciences, so it’s clearer when someone’s making obvious mistakes, cutting corners, or making under-supported claims. That makes it difficult to do poor work. It’s also difficult to good work, of course. The easiest thing to do in the hard sciences is to meet a minimum level of competency and do solid but uninspiring work.
Meanwhile in the soft sciences there’s questions even about the field’s basics. There’s still a minimum level of competency, but it’s much less stringent than in the hard sciences. So sloppy researchers tend to end up in the soft sciences.
Here’s another way to approach the hard/soft distinction. What’s easier, formulating questions or answering them? It’s almost always easier to do the latter, provided you’ve very clearly and specifically formulated your question. Of course we seldom do get our questions right on the first try, and so answering them involves going back over and over again and updating our hypotheses, which makes answering questions feel hard. But the hardest parts of answering questions are really secretly still about asking them.
In the hard sciences, it’s easier to clearly and specifically formulate questions because so much knowledge has already been established. Isaac Newton famously said (paraphrased) ‘If I have seen further it is only by standing on the shoulders of giants.’ The hard sciences are full of giants, with shoulders for modern researchers to stand on. The soft sciences are by and large still on the ground.
For this reason, I prefer the terms “developed” vs “undeveloped” sciences. I think it comes closer to the essential difference.
Note: this post has an update/correction post.