“Unlike freedom of speech, freedom of thought seems to be a natural attribute of humans. After all, thoughts are, by contrast to words, both inaudible and invisible – and therefore they appear to be beyond the grasp of censors. […] In fact, the conviction that thoughts are really free is deeply rooted in different languages. For example, the famous Latin maxim Cogitationis poenam nemo patitur appears in English as Thoughts are toll-free, in German as Gedanken sind Zoll frei and in Polish as Myśli są wolne od cła. In sum, this maxim says that nobody can be punished for his thoughts, no matter how iniquitous they may be. Even though the assertion seems true, the problem is not so simple as it looks.”

From the Introduction