It will be convenient for the argument if, instead of at once entering upon the general thesis [the defense of various individual liberties], we confine ourselves in the first instance to a single branch of it on which the principle here stated is, if not fully, yet to a certain point, recognized by the current opinions. This one branch is the Liberty of Thought, from which it is impossible to separate the cognate liberty of speaking and writing. Although these liberties … form part of the political morality of all countries which profess religious toleration and free institutions, the grounds, both philosophical and practical, on which they rest are perhaps not so familiar to the general mind … Those grounds, when rightly understood, are of much wider application than to only one division of the subject, and a thorough consideration of this part of the question will be found the best introduction to the remainder.