Just imagine for a second.
The book is an iPad which instead of a screen has paper leaves which may be turned, and contains no plastic.
The pen is an extension of your fingers which comes between you and your thumb.
Paper is a touch screen without the capacity for self-erasure.
The library is a website with very low page-loading speed.
A definition has two parts: the genus (family) and the differentia (specific difference). This type of definition is a given of logic and mathematics and it’s called intensional. It narrows down the identification as much as possible. It’s not the only type of definition, but it’s the most common.
Its structure does not shift. Families and differences do. The family tracks most of the cultural change, because the family is not just the closest category (proximate genus), but also the guiding notion, the most familiar bit of the concept under definition. The iPad is a tablet which. We know what a tablet is, phew. Then we can move to what sets it apart. We get ready for a new concept gradually, by starting from the familiar and moving into less familiar territory, until we’ve made it our own. Then we develop something new, and create a new definition.
So back to ‘the book is an iPad which’. It sounds funny now, but if books were to become obsolete, we’d have to reinvent them, and to find new definitions.