Although our modern practice of reading is essentially a solitary pursuit, there's comfort in knowing I'm not alone. More than reading groups, seminars, and the awareness that the offices around me are full of other grad students diligently reading, sometimes books lent by professors or picked up from the library provide another kind of companion.
I'm ambivalent towards my absent reading companions. Sometimes, especially in library books, it seems like a dozen of them are yelling in bright greens, blues, yellows and oranges, begging to pay attention to what they're interested in. At others times, there's a sense of abandonment when they suddenly disappear after an introductory chapter or section, leaving me to work through the meat of the book alone.
Sometimes my fellow reader, though separated by space and time, is someone I know, someone whose advice I find valuable, and who I always leave conversations feeling smarter for having engaged with. These are books from professors or classmates, whose scribbles, underlines, check marks, exclamation points, and other various marginalia give me deeper insight into where they're coming from, what ideas make them tick or scream.
This is not to say that my anonymous companions don't provide similar insights (Why, I asked my absent companion, are you upset about the use of the term "dark ages" but not the use of "man" to mean "humanity"?), but though we're brought together in the artifact of the book, the insight is less personal and more fleeting.