“To be happy means to be free and to be free means to be brave,” Pericles said in his oration for the Athenian war dead. The ancient Greeks treasured parrhesia, which can translate as “free speech” or “all speech” or “true speech”. Whatever version you prefer, it always carried a notion of courage with it.

The 20th-century French philosopher Michel Foucault developed the theme and argued that speech was only free when the weak used it against the strong. In parrhesia, the speaker chooses “truth instead of falsehood or silence, the risk of death instead of life and security, criticism instead of flattery and moral duty instead of self-interest and moral apathy”. On Foucault’s reading, the worker who criticises his boss uses parrhesia. The boss who shouts down his worker, does not. The woman who challenges religious notions of her subordination is a parrhesiastes. The clerics who threaten her with ostracism or worse are not. In the Chinese legend, the mandarin who knows he must contradict the emperor orders carpenters to build him a coffin and takes it with him to court. Pericles would have approved.

We like to think of ourselves as speakers of truth to power.

Nick Cohen’s argument for whistleblower protection proceeds from a classical argument for freedom of expression.