I'm even less clear on what a "meaningful cluster in conceptspace" means than I am on the traditional philosophical formulations of the problem. What would a "meaningless" cluster in conceptspace look like? Is there a single unique conceptspace, and how is it defined?
Good philosophers must beware of equivocation. Universal is an ambiguous term, so taboo it and distinguish several things it's stood for:
predicate - term that can be applied repeatedly. (If 'nominalism' is meant to reduce all universals to predicates, then it's an ill-conceived project, since it seems to be trying to explain commonality in general by reducing it to commonality between words; but if the latter is left unexplained, then commonality itself is left unexplained.)
common nature - something intrinsically possessed by all the entities that share a property. An abiding 'essence,' some kind of 'quarkhood' that inheres in all the quarks. Common natures are a posit to explain similarity. They are worldly, thus completely unlike Platonic Forms.
common cause - a single cause that has multiple effects. A Form acts as a common cause, but not a common nature, since on Plato's view they causally produce the recurrence of nature's patterns 'from the outside.' (In some ways, they're an anthropocentric precursor to Conway's Game of Life.) Like common natures, common causes can be posited with the intent of explaining why our universe exhibits similarity. If the question 'Why do properties recur at all?' or 'Why are some characteristics of the world the same as each other?' is well-formed, then there is nothing mysterious or ill-conceived about these posits, though they may perhaps by theoretically unnecessary, unenlightening, or ad-hoc.
Part of the sequence: Rationality and Philosophy
Bertrand Russell
I've complained before that philosophy is a diseased discipline which spends far too much of its time debating definitions, ignoring relevant scientific results, and endlessly re-interpreting old dead guys who didn't know the slightest bit of 20th century science. Is that still the case?
You bet. There's some good philosophy out there, but much of it is bad enough to make CMU philosopher Clark Glymour suggest that on tight university budgets, philosophy departments could be defunded unless their work is useful to (cited by) scientists and engineers — just as his own work on causal Bayes nets is now widely used in artificial intelligence and other fields.
How did philosophy get this way? Russell's hypothesis is not too shabby. Check the syllabi of the undergraduate "intro to philosophy" classes at the world's top 5 U.S. philosophy departments — NYU, Rutgers, Princeton, Michigan Ann Arbor, and Harvard — and you'll find that they spend a lot of time with (1) old dead guys who were wrong about almost everything because they knew nothing of modern logic, probability theory, or science, and with (2) 20th century philosophers who were way too enamored with cogsci-ignorant armchair philosophy. (I say more about the reasons for philosophy's degenerate state here.)
As the CEO of a philosophy/math/compsci research institute, I think many philosophical problems are important. But the field of philosophy doesn't seem to be very good at answering them. What can we do?
Why, come up with better philosophical methods, of course!
Scientific methods have improved over time, and so can philosophical methods. Here is the first of my recommendations...
More Pearl and Kahneman, less Plato and Kant
Philosophical training should begin with the latest and greatest formal methods ("Pearl" for the probabilistic graphical models made famous in Pearl 1988), and the latest and greatest science ("Kahneman" for the science of human reasoning reviewed in Kahneman 2011). Beginning with Plato and Kant (and company), as most universities do today, both (1) filters for inexact thinkers, as Russell suggested, and (2) teaches people to have too much respect for failed philosophical methods that are out of touch with 20th century breakthroughs in math and science.
So, I recommend we teach young philosophy students:
(In other words: train philosophy students like they do at CMU, but even "more so.")
So, my own "intro to philosophy" mega-course might be guided by the following core readings:
(There are many prerequisites to these, of course. I think philosophy should be a Highly Advanced subject of study that requires lots of prior training in maths and the sciences, like string theory but hopefully more productive.)
Once students are equipped with some of the latest math and science, then let them tackle The Big Questions. I bet they'd get farther than those raised on Plato and Kant instead.
You might also let them read 20th century analytic philosophy at that point — hopefully their training will have inoculated them from picking up bad thinking habits.
Previous post: Philosophy Needs to Trust Your Rationality Even Though It Shouldn't