In particular, I'm thinking about how to define and defending radical feminism. If by radical feminist one means `someone who thinks Andrea Dworkin and Catharine MacKinnon got a lot of things right', then I'm probably a radical feminist. But that's not really a helpful definition to bandy about when using the term around the almost everyone who has never read either Dworkin or MacKinnon. (Or thinks that what they said can be accurately summed up as `all heterosexual sex is rape'.)
Here's my proposed definition:
Radical feminism is the thesis that our gender* categories, in themselves, constitute a fundamental system of injustice.
I like this, first of all, because it's fairly short, but makes a strong and controversial claim. Let's unpack it by contrasting it with alternative positions.
First, antifeminism. The antifeminist denies that there is any gender injustice in our society. This leads almost immediately to the MRA complication: Men's Rights Activists such as Warren Farrell say lots of antifeminist things, but still believe in gender-related injustice. However, I think their position is easily turned, ie, the solution to most of the problems they identify (unjust divorce and child custody laws, discriminatory selective service laws, &c) is more feminism, not less. The fact that it's called feminism doesn't mean it is indifferent to any oppression suffered by men. In any case, by contrast with both radical feminism and MRA positions, antifeminism believes that everything is just dandy with respect to gender.
Second, there isn't a good term for this position, so let's just call it supervenience feminism. Supervenience feminism agrees with radical feminism that there is gender injustice, but claims that this injustice supervenes on other kinds of injustice. Marx's analysis is the prime example I have in mind. Marx claims (somewhere; if anyone has the cite handy, please share in the comments) that gender injustice in a society is a good way to identify economic injustice: the worse off the proletariat (men) are, the worse the domestic violence and rape. We can expand this analysis into a stronger claim (which, just to be clear, I do not believe Marx made), viz, if we `just' solve this problem of economic injustice, then all the gender injustice will disappear, too. By contrast, radical feminism, with its claim that gender injustice is fundamental, rejects this analysis. Gender injustice does not supervene on any other system of injustice, though it can obviously interact with other systems.
Third and finally, what I will (somewhat inaccurately, but with good reason) call liberal feminism. Liberal feminism agrees with radical feminism that gender injustice is real and forms a system of injustice which cannot be reduced to, though intersects with, other systems. But liberal feminism does not agree that our gender categories are in themselves unjust. According to liberal feminism, our gender categories are more or less fine in themselves, but have been utilized in constructing a system of oppression.
Thus, consider high heels (a favourite point of controversy between liberal and radical feminists, though not as favourite as blowjobs). There is nothing wrong with high heels as a symbol of femininity, say the liberal feminists, at least not in themselves. The ridiculously high ones are ridiculous, of course, and no-one should go around wearing them all the damn time because they'll fuck up your feet, but there's nothing intrinsically wrong with wearing moderately high heels even regularly. The problem comes when high heels are regarded as compulsory (fancy dress occasions) and a justification for physically harming women (footbinding in feudal China, surgery to fit into pointed-toe shoes today). In these cases, a system of gender injustice has been grafted on to something which is intrinsically just fine.
The radical feminist disagrees. The radical feminist points out that high heels were specifically designed, and the fondness for them amongst women specifically instilled, for the ends of gender injustice, namely, the sexual objectification of women. High heels are a wholly original creation of patriarchy, not some innocent-in-itself appropriated by patriarchy some time after their original creation. And women don't freely choose from a Rawlsian Original Position to embrace high heels, only to discover once they are in society that they're used as tools of oppression. Women are taught from very early on that (a) they are primarily valuable as sex objects, and (b) one great way to increase their value as sex objects is to wear high heels. To borrow Marx's term, the radical feminist claims that a love of fashion in general is a form of false consciousness, not a justification for high heels in feminist utopia. (The problems defending a false consciousness claim may explain why there is so much debate over high heels and such: the radical feminist is unable to offer the liberal feminist a convincing argument on the latter's own terms.)
And now I'm really running late. Thoughts?
* There are two major complications here. First, sexism extends to both gender and sexual injustice -- the lack of research into female heart disease is a good an example of sexism which is sexual, not gender, injustice. Second, gender injustice has tight intersections with heteronormativity (especially), classism, racism, &c. So, properly, fighting gender injustice should be neither necessary nor sufficient for feminism. But I suspect this analysis is built on the mistaken idea that there is some kind of clear, precise, and accurate classification of systems of injustice and opposition to them. There simply is no fact of the matter about where feminism stops and queer activism starts. So, because, for any definition, some cases will be problematic, and because it's convenience and perspicacious, I'll just talk about gender injustice.