Yesterday, in my lecture class (Science in the United States), we ended up having a bit of a class discussion about the borders and boundaries of science. I love this type of question, and I think that we learn a lot about our own assumptions and categories when we try and work through possible answers. (For instance, when you start pushing people on this question, you find that many people think that if you say something isn't a science, you're saying that it isn't a valid field of inquiry, or that it isn't intellectually rigorous, or that it can't be right.) I think that some of the students found the discussion frustrating, but I thought it was interesting, and a couple of people told me afterwards that they hope we come back to this topic again.
After class, someone asked me what my own definition is--what do I think makes something a science, or not a science. I found it a really difficult question to answer, for a number of reasons. First of all, I don't think there -is- a clear and easy definition. There's not really a single bright line that can be drawn between "this type of work is science" and "this type of work is not science." It's also difficult for me because so much of my interest in the question is how -other- people answer it: I know why Albion Small thought that sociology was a science, and why G. Stanley Hall thought that psychology was a science, and why the judges in the Kitzmiller decision thought that intelligent design was not science. I know the arguments for (and against) including Renaissance European alchemy, dynastic Chinese medicine, Babylonian astrology, and Alexandrian engineering in the historical category of "scientific work". I can argue both sides of the question about whether modern Western medicine is scientific. And I've been known to think of the discussions about what constitutes "science" as a kind of inkblot test for what people think about different areas of research. At the end of all of that, though, where do I personally draw the borders and boundaries? I'm not sure I know.
I think that most of the time, when people try and drawn the boundary between science and not-science, they start from an instinctive or intuitive sense of which types of work are scientific, and then they back-form the criteria. Pretty much everyone agrees that physics, chemistry, and biology go in the "science" box, along with their associated branches and sub-fields. A lot of other disciplines are in a contested area, and a person's first intuitive or instinctive reaction as to whether these other disciplines (psychology, linguistics, engineering, computer science, sociology, economics, political science, medicine, archaeology, anthropology) go in the "science" box or not seems (based on my thoroughly unscientific sampling) to be based largely on her personal experiences. The sorting into boxes comes first, and on an unconscious level; the outlining of criteria (experimentation, quantification, verification, general laws, predictive power, falsifiability, etc.) comes second, as a way of trying to make sense of the way you've sorted things.
The way I sort things is based on my own history in this field. Ten years ago, when I was finishing an undergraduate degree in psychology, I probably would have sorted things differently than I do now; four years before that, when I was a smart-ass high school senior with big plans to be a physics major and equal passions for Greg Egan and Ayn Rand, I -know- I would have sorted things differently than I do now. Now, though, after six years in graduate school and two years teaching broad surveys on the history of science, I have very fuzzy boundaries for science. I'm willing to toss most things into the "science" box, as long as I'm allowed to keep up a running commentary on the arbitrary and historically-contingent nature of the definition. One snag in the sorting, though--the class reading that prompted all of this, the 1895 mission statement for sociology, makes reference to the "science of history", grouping history with economics and sociology, under the heading "social science."
Is history a social science? Maybe? It is (or should be) rooted in factual evidence, and it can (sometimes) look for generalized laws, and certainly there are plenty of people who would categorize it that way. There's a discussion down in the comments on this post about what it means to have a finding or a result in the humanities, and when I follow that reasoning through, I become more sympathetic to the idea that history (unlike, say, literature studies) can be thought of as a science. When I first came to Berkeley as a graduate student and attended the day-long orientation for new grad students, I waffled over the afternoon breakout sessions, whether I was supposed to attend the discussions for humanities students or the ones for social science students. When the idea of history as a social science came up in this reading, though, I found myself pulling away from it. Is this a type of science, what we do? My sorting instincts want to put it in the "not-science" box. If the sorting question is, as I suggested above, an ink-blot test, what does it say about me that I'm resistant to calling this work scientific, even though it meets some of the criteria that logically fall out of my sorting process?
I don't have an answer here, just a lot of questions, and the overall sense that the science/not-science question is one for which the best answers are more like a spectrum and less like a set of boxes.