The "pleasure" of which Aristotle speaks is more of an appreciation of the beauty of a work of art that embodies tragedy. I think that Aristotle is bringing out the idea that art, while it can depict the worst of consciousness, can be beautiful in this depiction. For example, art can display the most painful of conditions but do so in a manner whereby one can only express appreciation of it. When I speak with students about "favorite movies," I always indicate "Schindler's List" or "Sophie's Choice." Almost a patterned response that the kids have upon hearing this is, "That's so depressing! How could you like that!" I think that Aristotle's understanding of "pleasure" might be evident here. When a work embodies the principles that Aristotle attributes must be contained in an effective work, it is in this light that tragedy can contain a level of "pleasure" for the work has impacted the audience on both an emotional level of fully understanding the tragic predicament of the protagonist, and has done so in an aesthetic light where its construction has captured the audience's imagination.