First editions of to-day and how to tell them

the long version

"Generally speaking, the collector of first editions is realy a collector of first impressions, a first impression being a book from the frist lot struck off the presses and a first edition comprising all books which remain the same in content and in format as the first impression. A second impression is a second printing. A second edition postulates some alteration of text or format. But these terms are unfortunately, not strictly adhered to." "It is hoped that this book will serve to guide the collector admist these intricacies." -- From introductory note.