An open book
Meaning
A person whose thoughts, feelings, and intentions are easily understood and readily apparent to others.
Origin
Before mass literacy, books were treasured objects, often closed and their knowledge guarded. To open a book was to unveil its secrets, to lay bare its entire contents for all who could read. As books became more commonplace and literacy spread, this powerful image transformed into a metaphor for human transparency. By the 18th century, describing someone as "an open book" conjured the vivid picture of a person whose innermost thoughts, feelings, and intentions were as plainly visible and easily understood as the words on an opened page, with nothing hidden or concealed.
Examples
- My sister is an open book; you never have to wonder what she's thinking because she tells you everything.
- Despite his quiet demeanor, the artist was an open book, expressing all his emotions freely through his paintings.