The ones worth owning rather than borrowing, in editions built to be reread.
A classic on this shelf has to earn its place as an object too: sewn binding where we can get it, a typeface that survives a long evening, margins wide enough to write in.
We will happily tell you which cheap edition is fine, and which one will fall apart in a term. Both answers come up often.
Not sure where to start? Tell us the last book you finished and roughly how it went. That is usually enough.
Ask a bookseller