It's often cited that the writing sample is the most important part of the application.
But what kind of sample exactly are committees looking for? I've heard "near-publishable quality" sometimes as a standard, but is that really true? Very few undergraduates publish philosophy, and some graduate students don't either. So is that really the bar they're using to review papers, especially in a 10-20 page sample?
Additionally, is there something specific that committees prefer to see? E.g., is the expectation that you demonstrate some kind of breadth of philosophical knowledge, e.g. awareness of various debates from major areas like epistemology, metaphysics... or can you simply write an original argument on an interest area and defend it well?