At the end of his “Introductory” chapter of On Liberty, in paragraph 16, John Stuart Mill writes:
It will be convenient for the argument, if, instead of at once entering upon the general thesis, 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, recognised 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 of writing. Although these liberties, to some considerable amount, 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, nor so thoroughly appreciated by many even of the leaders of opinion, as might have been expected. 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. Those to whom nothing which I am about to say will be new, may therefore, I hope, excuse me, if on a subject which for now three centuries has been so often discussed, I venture on one discussion more.
To me, this is a reminder of the importance of making the argument for the things we believe in. If people take for granted the idea that freedom of speech is a good thing, without having ever made or heard the argument, their commitment to freedom of speech can easily wilt under the heat of the first temptation to abridge someone’s freedom of speech. If people take for granted the idea that free trade is good, without having ever made or heard the detailed arguments for that idea, they are likely to think free trade is good except in every special case that is actually at issue in public debate. If people say science has proved evolution without actually knowing all the powerful arguments in favor of evolution, they are just attempting to substitute one authority for another, without realizing that the essence of science is in the detailed reasons it gives for its claims, and in the ability to investigate those reasons more and more deeply.
One of the most interesting arguments that John Stuart Mill gives for freedom of speech in the following chapter is that freedom of speech helps to force people to actually make arguments and keep the knowledge of those reasons alive, instead of letting those reasons become simply the reasons that dead men had for believing something, while our reason for believing it becomes simply that they did.
Those of us who are teachers, and perhaps in especially great measure, those of us who are teachers in colleges and universities, are remiss in our duties if we do not give students the arguments for believing what we believe. We might be tempted to think that teaching them the right ideas without backing them up will do the trick, but at some point in the lives of college graduates, when something that was abstract in college becomes real and concrete, and the thinking begins in earnest, the trains of thought that back up an idea might be more robust in the face of those motivated to confuse an issue than the memory of a professor’s simple assertion of an idea and testing of the ability to memorize that idea for an exam. None of this is easy. But I fear that failing to give reasons builds an education on sand, and the house built on the sand will soon wash away.