To some degree, good philosophical writing is a matter of taste. In my courses, however, I will generally ask you to write in particular genre and with particular goals in mind. So let me say a bit about writing in this genre.

A good philosophical essay is neither a manifesto nor an unfocused series of opinions. Only very rarely is it simply a description of someone else’s argument (though this may be involved). It should be a serious attempt answer a particular question — to stake out an interesting position on an issue that is worth thinking about. In my entry-level classes, usually I'll give you the question so you can focus on developing some basic analytical and argumentative skills. In 200-level courses and above, I will often ask you to "ask your own question". At this level, students should be working on turning the corner from being consumers of knowledge and understanding to producers of it. Whatever your level, however, your focus should be on your essay's argument. Gone are those heady, carefree days of competent summary — of “compare and contrast”. I expect essays of an entirely different caliber. Here's some general advice to help you get there.

Choice of Thesis and Openness to Change
Here's a way of thinking about choosing and developing a thesis: it should be an answer to a question worth asking. How do you know when a question is worth asking? In the ordinary ways: ask yourself, is the answer obvious? Does (or should) anyone care — why? Part of your job may need to be helping your reader appreciate your thesis's significance. A good test of a thesis is whether someone could conceivably disagree with it. If such disagreement is hard to imagine — e.g., because the thesis is too vague or something that most people already believe — then there's no much point in arguing for it! (see the sidebar for common problems with theses). 

Practically speaking, it's  crucial to identify a question that can be answered in the space you have allotted. One of the most common problems I see in essays from less experienced writers is that they choose a question that's so big and complex that it'd take a book to properly answer it. Your thesis thus sets the terms for your essay's success. 

Sometimes writers lose faith in their thesis as they write — perhaps as they attempt to put their arguments down on paper and see that they have some holes. In this case, it's usually a bad idea to force things. Be open to changing your mind on the strength of your own argument. Allow yourself to scrap the bulk of a paper in order to accommodate your real message as you discover it. ​For this reason, I often suggest not spending a lot of time polishing the first paragraph or two of your essay until you feel confident of where you're headed. It's sometimes better to just dive right in to the argument and let the nuance of your thesis develop as you go. 

Your Argument
Ideally, a piece of philosophical writing should be “one long argument” (as Darwin described his Origin of Species). Arguments have premises and a conclusion. Your thesis is your conclusion; your premises may be commonly-accepted claims, assumptions, or conclusions of other arguments that you make or reference. In any case, you should make clear what your premises are and why you think your reader should accept them. Since you can't argue for everything at once, it's often a good strategy to simply note when you are assuming something without argument because it seems to you very plausible.

You should also take time to be clear about how your argument works. Explain its structure carefully and show why it is valid (if you are able to offer a deductive argument). Ordinarily, an essay will contain many sub-arguments: you might describe someone else’s argument, you might argue that tempting objections to argument X fail, you might argue that because argument X fails we ought to accept argument Y, and so on. Acknowledging contrary viewpoints is often an invaluable philosophical tool. If you are defending a substantive enough thesis, there are bound to be objections to it. Articulate such objections (a representative one or two, perhaps) in the strongest way you can. Your argument is strengthened by successfully rebutting well-conceived objections. Conceiving a weak opponent (a "straw man") has the opposite effect. It is often better to express contrary opinions as strongly as you can. Don't be afraid to acknowledge hesitation or concerns: we can’t always offer knock-down arguments for interesting theses (even for those theses we ourselves hold). Better to acknowledge weaknesses in your position rather than trying to cover them up and leave them for someone else to expose.

Bear in mind what does not count as an argument: that something seems clear to you, that something seems clear to some eminent philosopher or other, that what you say is (more or less) consistent, and so on. Again, your job is to convince your reader.

Style & Mechanics

Formatting
I have written a more substantial Guide to Formatting. If you are in one of my classes, I will ask that you follow it. If you're not, take it or leave it. It's just a convention.

Reference Lists
Unless otherwise instructed, your essays must — I repeat — MUST include a References list. Conventions dictate which citation conventions to follow. Me, I don’t care much so long as you’re consistent, you italicize books, enclose article titles in quotes (see Formatting Guide for my preferred style). And bear in mind that not everything should be used as a source — though everything used as a source must be cited (if it’s not, it’s plagiarism). Don’t rely on anonymous postings, wikipedia, websites/blogs (like mine), notes on napkins, &c. A good rule of thumb is: only use sources that are peer-reviewed in some way. That rules in obvious cases like the various online philosophical encyclopedias (the Stanford Encyclopedia of Philosophy, the Internet Encyclopedia of Philosophy, or the Routledge Encyclopedia of Philosophy) or online pre-prints of papers accepted for publication in peer-reviewed philosophy journals often available on philosophers’ websites (like mine), and so on.

General Writing Advice
I’ve thought a lot about writing well (trying to write well myself and trying to teach students how to write well). While I seriously doubt that there’s a formula, I’ll offer you a few pieces of advice that I’ve found particularly useful.
 
Persequere sollum pullum.
That translates roughly to "choose your chicken".

While I haven't had the pleasure of trying to catch a chicken, I understand that it's almost impossible unless you just go after one. Otherwise you're drawn in different directions: one gets away because here's another that's closer . . . and here's another!. . . . In the end, you come up empty-handed.

I hope the analogy for essay-writing is clear. You'll ultimately fail to do anything if you try to do everything (or even just a few things!). Resist the temptation to write on every neat idea that pops into your head. Imagine instead that a skeptical and curmudgeonly reader looking over your shoulder mumbling: “So what?”, “Why’s that relevant?”, “You haven’t convinced me of anything yet — you’re just making a bunch of undefended claims!” Head off these objections. Focus.

Spread your work out over many drafts. Writing something worth reading is not generally something that happens on a first draft. When I write, the first stage is usually just getting ideas down and exploring the territory a bit. Give yourself as much time as you can to let the ideas percolate. It can seem an impossible task (and thus best avoided) until you just dive in, if only to think about what you want to write. Experiment: start by jotting down notes, typing interesting passages, quotes, aphorisms — then work up to a more coherent outline. By that time, you’ll probably have a better idea of what you want to say about an issue.

Subsequent drafts shape and refine this raw material, improving clarity and focus. Especially in short essays, you must be a merciless editor. Once you get your notes/scraps into rough draft form, let some time pass — go for a run, play some basketball, watch a movie. Go back later with a clear head and empathy for your audience revise. Don’t resist getting rid of neat sentences, paragraphs, or whole pages that don’t fit. Try rewriting sentences using as few words as possible — imagine that words are a scarce resource.

Write not only so that you can be understood, but so that you cannot be misunderstood. One of the worst vices of philosophy (and unfortunately, one of the most difficult to avoid) is falling into unclarity. This typically occurs when your argument relies on poorly terms, vague ideas, and pointed questions. Often, unclear writing devolves from an attempt to write "like a philosopher". Bad idea: many philosophers — including famous, great philosophers — are dreadful writers. The best philosophical writing is admirably clear and can be read and understood by anyone. Again, imagine a good-hearted curmudgeon reading your essay; ask yourself while writing whether it would be clear to most people with just a little exposure to these issues.

Take the Read-Out-Loud Test. By a third or so draft of your essay, go through the painful exercise of reading it aloud to yourself. Seriously. Better yet, have someone else read it aloud to you; or read it to someone else if you can stand it. If something doesn’t sound right or isn’t clear, change it. You’ll feel silly, perhaps, but never mind — I guarantee that you’ll find plenty to change. Jonathan Bennett (an eminent philosopher emeritus at Syracuse) recounts writing to a graduate student:
Gilbert Ryle once told me, ‘What doesn’t read well to the ear doesn’t read well to the eye’, and that changed my life. More than any other one thing, that insight showed me how to start climbing out of the garbage pit up onto the plain of decent prose. I had some of my material read to me while I listened with my eyes closed, was appalled by how ugly and boring it was, and took action. . . . I recently sat in my study at home and read my book The Act Itself aloud in ringing tones, imagining an audience and aiming to do the performance with gusto. Whenever my confidence ebbed and my voice wavered because the prose was not moving properly, I rewrote. For your first few professional years, though, I urge you to submit yourself to the discipline of listening to your own prose without at the same time following it on the page.
Hear hear! Aim for clarity and plain language. Avoid elaborate constructions and the passive voice when possible. An excellent philosophical essay conserves words, avoids colloquialisms, and uses the active voice. (Rule of thumb: minimize use of the verb ‘to be’ — ‘is’, ‘are’, ‘was’, ‘will be’, ‘has been’, &c.) A brisk and clean prose always achieves more than rhetorical flourish. That does not mean that a good paper must be boring. Just let the interest reside in the ideas and not the challenge of working through a maze of overly complex constructions or flowery metaphor. Note as well that humor in this context can be very tricky, though again, it can be effective if used judiciously.

First person reference is acceptable when unobtrusive (e.g., “I find Plato’s argument unconvincing for the following reasons” or “We must ask next whether Plato can support this claim”), but don’t go overboard with autobiography (“It first dawned on me that laws of nature were subjective one morning when I. . . .”). You have to judge for yourself how much “autobiography” is tolerable and relevant. Try to find a clear, concise philosophical voice.
​Writing Resources
There's a lot of good stuff out there besides the content of this page that I'd encourage you to look at. Here are my highlights:
Common Thesis Problems
  • The Boring Thesis: The boring thesis either answers a question not worth answering or doesn't even clearly identify a distinctive question to answer at all (e.g., by merely summarizing someone else's view). Test to see if you've moved from summary to critical analysis/argument by articulating the interesting question you're trying to answer and asking whether it was worth asking. Is it the kind of question where someone might respond "Huh. . . . I don't know. I'll have to think about that."? That's what you want.

  • The Boring Thesis (Obscurantist Gambit): Sometimes writers will (accidentally or otherwise) disguise the fact that their thesis is patently obvious, unsurprising, and something everyone would readily accept by dressing it up in hyperbole and obscure language. This strategy is bound to fail for readers unimpressed with big words and complex constructions. For even if one manages to obscure the fact that the thesis is trivial, it’s still obscure what’s being claimed — and thus a failed essay.

  • The Over-Ambitious Thesis (Negative Version): For example, you might regard some problems facing a particular philosophical view — say, Platonism about properties — as pretty serious. Fair enough. But to argue that the Platonism is false is a tad ambitious. To really accomplish that feat, one would presumably have to run through many objections in detail, attending to potential replies or minor modifications of Platonism and possible weaknesses in your approach. And even then, doubt may remain. Set yourself up to succeed by narrowing your focus — e.g., by attending to just one problem in detail.

  • The Over-Ambitious Thesis (Positive Version): Sometimes, I see the Over-Ambitious Thesis manifest itself in a positive essay. “Finally!” you say to yourself, “an opportunity to lay down my thoughts about the true nature of Reality!" Don’t get me wrong here — ambition can be good. But effectively arguing for a positive thesis requires great care and modesty. Arguing for something really big doesn't happen easily. You have to make sure you attend to possible problems, objections, and weaknesses in your argument (being a curmudgeon comes in handy here). This takes time. Remember: your thesis sets the terms of your success.

  • The Weaseling Thesis:  
    The weaseling thesis looks like a stand on some issue, but evades responsibility by using vague terms or stating the obvious.

    Examples:
    (a) “Plato and Aristotle both agree and disagree about the nature of the soul.”

    READER RESPONSE: “How, specifically, do they agree and disagree — and why?”

    (b) “Throughout human history, people have confronted issues raised by social inequality”

    READER RESPONSE: “Which people? What issues? Is this author really going to discuss all of human history in these few pages?”

  • Grandiose Proclamations:  
    A close relative of the Weaseling Thesis, the Grandiose Proclamation is a way of spinning wheels and burning words. E.g., “The history of Western Civilization — nay, of Civilization tout court — consists of a series of rises and falls of great ideas.” [yawn!] Such statements, aside from being pretentious and pompous, are simply boring. Don’t waste words on the trite, false, and indefensible. Get right to the point; make it specific and manageable.

  • Lack of Thesis: 
    This is the cardinal sin of philosophical writing. Proposing a boring, weaseling, over-ambitious, or grandiose thesis is one thing; no thesis at all (unless so requested) is a scandal.