All philosophy is philosophy about something, and in theory we can consider everything philosophically. But the value of a philosophical investigation is defined partly by its subject matter, and some topics make for better philosophy than others. One mistake that is rarely made by philosophers is picking a topic that is too specific. For example, few philosophers would be inclined to philosophize about what the tallest mountain is. Which is not to say it is impossible to attempt to apply philosophy to such a question, it is just that the philosophical investigation about it is rather short. It might, for example, begin by considering what is meant by “tallest”, and how heights can be compared when there is no single length that the two objects can be directly compared to. Such questions, however, have been already answered, and so this philosophical investigation quickly yields the conclusion that we can determine which is taller by measuring air pressure, or some trigonometric method. And thus such investigations are relatively valueless because the important issues involved have already been settled. In general any issue for which there is a clear way to determine the answer in a scientific fashion is too specific; the philosophy is essentially done already.
But, as I indicated, accidentally working with a subject that is too specific is a rare occurrence, most of us have a fairly reliable conception about which questions science is and isn’t in a position to answer, and we steer clear of the ones that it is for fear of making fools of ourselves by giving the wrong answer to them (insert Hegel joke here). However, going too far in the other direction, and dealing with subjects that are too abstract is a common mistake to make, and one that may not even be admitted as a mistake by some.
But before I argue that investigating topics that are too abstract is a mistake allow me to first describe in detail what exactly is the proper range of subjects for philosophical investigation, and thus defining in that way what counts as too abstract. In any philosophical investigation we will make claims, that of two possibilities one is the case and the other isn’t, that a certain way of analyzing that subject matter is superior to the others. We must always ask ourselves, about these claims “so what?” For every claim we make about our subject we should be able to identify consequences if we are right, and consequences if we are wrong. And, most importantly, both sets of consequences should matter to people in general, not just philosophers. If we are unable to identify such consequences then it implies that our philosophical thinking has wandered off track, that we have built for ourselves an edifice of words that has no real significance. Of course whether such considerations should impact how we do philosophy depends on your attitude towards philosophy as a whole. If you treat philosophy as a purely private matter, something that you keep to yourself, then indeed whether it has any impact on other people doesn’t matter. But the vast majority of philosophers make their work public, which implies the belief that others might understand their work and be affected by it, and to do philosophy in a way consistent with the practice of publishing it necessitates caring about whether our claims do actually matter to people other than ourselves.
Now this is not meant to be a criticism of philosophy. Indeed I think that most of the persistent philosophical questions, those that philosophers from every generation address in their own way, persist because the claims about them matter. For example, ethics is clearly something that matters. To say that something is unethical is to say that we should stop doing it, while to claim the opposite, to say that it is ethical means that we are free to continue (barring, of course, any other reasons to stop). Similarly most epistemological questions are also relevant. Deciding what to believe is important because having beliefs that you shouldn’t, or failing to have had beliefs that you should, will lead, at best, to missed opportunities, and at worst to disaster. And political philosophy and questions about social justice also have consequences that concern most people, since we are almost all part of some society how we organize ourselves as a society matters to us. Of course I don’t mean to limit this list solely to matters that are immediately practical. I wouldn’t, for example, deny that investigating the nature of consciousness matters. Of course investigating consciousness matters not because it has immediate consequences, but because many people, not just philosophers, are genuinely curious about what it is. And, because we care about consciousness, studying it can have a number of secondary implications, determining who and what is conscious may impact how we treat them. However, it is important to keep in mind what makes these investigations matter, why people care. While people are curious about the nature of consciousness, because it is something they encounter daily, people are not genuinely curious about the nature of knowledge, what they want to know is which of their beliefs are most likely to be true. And thus an account of the nature of knowledge matters only to the extent that it impacts where it agrees and disagrees with how we are already deciding which beliefs to treat as true.
Thus a topic that is too abstract is one that people in general are indifferent to the claims we make about it. For example, most people are indifferent concerning whether objects have individual essences. If you assert that objects do have individual essences no one but a philosopher can see that as important, and similarly hard to get people to care about a denial of the claim. Now this doesn’t, in an absolute sense, forbid addressing such topics, but it does show that if we are to address them it must be because they are linked to something that matters. For example, if it could be shown that the claim about individual essences, perhaps in conjunction with some other premises that are believed to be true, has implications for how we should act in certain circumstances then the claim would matter, it would have consequences that people care about. But, while we aren’t forbidden from thinking about these claims, we are blocked from making them the center of our investigation, we are compelled to investigate things that matter by themselves, and only through these investigations arrive at such abstract topics.
But perhaps you aren’t compelled by my argument that philosophy should matter, maybe you approach philosophy as a purely intellectual exercise, serving no master but itself. Even if you take this approach there is still an argument against doing philosophy that is completely unconnected to things that matter to the majority of people: such philosophy is essentially impossible to validate. Sure you can argue for such a technical philosophical position, but every argument has premises that are themselves undefended, and so no argument is absolutely secure (especially abstract philosophical ones that aren’t grounded in facts that can be determined by observation). Thus the best way to evaluate a philosophical position is not by considering the arguments put forwards for and against it, but considering the claims themselves. Now when we are dealing with claims that matter to us it is always that case that they matter to us because they are connected in some way to facts about the world we live in. For example, to say that we should do something is to assert that the people who follow that advice will be better off, in some way. And thus we can directly examine the validity of the claim itself simply by considering people who do follow that advice to those who don’t and seeing whether they are better or worse off. Obviously this connection isn’t precise and scientific, but it does exist, and through it we can at least get some rough sense about whether the claims are correct. But without some connection to things that matter it is not clear how a philosophical claim could ever be evaluated by itself, and so we are left without any way to really know whether it is true or false. So, not only are we building an edifice of words that matters to no one but ourselves, but we are building an edifice that no one, not even its creators, can determine to be structurally sound.
Now for most people just starting to consider things from a philosophical point of view these warnings are unnecessary. Most people are motivated to do philosophy because they desire answers to certain question that matter to them, and since they are like many other people the questions that matter to them probably matter to a wider audience as well. However, the study of philosophy has a way of luring people away from the questions that really matter. To avoid this I have two pieces of advice. First never publish anything that contributes or builds off of a philosophical squabble (a back and forth argument about whether some argument or analysis is correct). Worrying about a philosophical squabble is worrying about whether a particular piece of philosophy is correct, and that is something that simply doesn’t matter (except to those already directly involved, philosophers and not people in general). If the philosophical squabble sparks your interest, and you think one side or the other is right, then it is better to simply address the subject matter that started the squabble in the first place, and contribute to the issue by what you have to say about that subject matter. And, secondly, if you can’t explain to non-philosophers what you are investigating and why by encapsulating your investigation as it is then you are doing something wrong, and need to refocus on what matters. (If, for example, you have to spend most of your time explaining what you are trying to say rather than why it matters, or simply can’t bring people to understand you, then you are almost certainly doing something wrong. Even complicated physics can be explained in general terms to most people so long as you leave out the math, and certainly philosophy is simpler than theoretical physics.)
Finally, allow me to conclude by taking my own advice and saying why this investigation matters. Why should anyone care about how we go about philosophy? Well, if philosophy matters, or at least has the potential to matter, then certainly how we go about it matters, just as the scientific method matters because science matters.