Starting from the principle that “It is not possible […] for a man to abdicate his thought and submit it absolutely to that of others”, Baruch Spinoza introduces the idea of freedom of expression.
Chapter XX of Baruch Spinoza’s Theological-Political Treatise (commonly abbreviated TTP) is subtitled:
“It is established that in a free state everyone has the right to think what he likes and to say what he thinks.”
The objective is indeed there: One can say what one wants, because one can think what one wants, and one can say what one thinks. The freedom to think is put first, then the freedom to be faithful to one’s thought, that is to say the freedom of expression. Because nobody can keep his thoughts secret.
Extract from the same Chapter XX:
If, then, no one can abdicate the free right he has to judge and feel for himself, if each person, by an imprescriptible right of nature, is the master of his own thoughts, does it not follow that it will never be possible in a State to attempt, without the most deplorable consequences, to compel men, whose thoughts and feelings are so diverse and even so opposed, to speak only in accordance with the prescriptions of the supreme power? Do the most skillful men, to say nothing of the people, know how to keep silent? Is it not a defect common to all men to confide to others the designs which they should keep secrets? It will therefore be a violent government that will deny citizens the freedom to express and teach their opinions; it will be a moderate government, on the contrary, that will grant them this freedom.
Baruch Spinoza – TTP – Chapter XX
It is even in the interest of the State not to censor opinions.
If we want to obtain from citizens not forced obedience but sincere loyalty, if we want the sovereign to keep a firm grip on authority and not be obliged to bend under the efforts of seditionists, we must of necessity allow freedom of thought, and govern men in such a way that, while they are openly divided in their sentiments, they nevertheless live in perfect harmony.
Baruch Spinoza – TTP – Chapter XX
Indeed, citizens can think what they want anyway. If they are forced to speak differently from what they think, good faith will be lost. But good faith is essential to the state.
Finally, let us recall that Baruch Spinoza himself experienced at close quarters the consequences of a lack of freedom of expression, rather by the religious authorities than by the state authorities, when he was expelled from the Jewish community for heresy.