There are no particular limits on subjects , though I try to refrain from venting opinions in public on matters about which I know little or nothing. Since 1998 I've gotten review copies from some publishers. I add a disclaimer to those reviews mentioning this. The contents of the reviews are entirely my opinions. I kept it up because I've found it a good way to clarify my own thinking about what I've read, because some people have been kind enough to tell me I'm good at it, and because I like spouting off.
Editors are often particular about citation formats, however.
They're the only medium I really know enough about that my views are at all worth listening to. I have credentials in physics , math , and some parts of computer science , chemistry and engineering. I've taken survey courses in cognitive science, neuroscience and general psychology, which is a completely inadequate basis for writing about them. So long as we're playing the humiliation game, I may as well confess to never having read Moby Dick or Henry James, and to never having gotten beyond page 100 of Gravity's Rainbow, despite three tries. All told, a shocking series of omissions for someone with a bachelor of arts degree.