Isn't That a Principle of Science?

In Newtonian science, there were no strong restrictions on what kinds of forces could have physical effects. But through the 19th century, investigations in the foundations of physics to do the conservation of energy found that there weren't any forces apart from nuclear forces and electromagnetic force. There didn't seem to be any effects anywhere, even living bodies, that couldn't be explained by those forces. Now, it's not cut and right. I mean it's kind of in principle possible that lurking in the interstices of our brains are some special mental forces that they haven't noticed yet. It seems to be an awful lot against such a theory.