"Our Nation is deeply committed to safeguarding academic freedom, which is of transcendent value to all of us, and not merely to the teachers concerned. That freedom is therefore a special concern of the First Amendment, which does not tolerate laws that cast a pall of orthodoxy over the classroom. "The vigilant protection of constitutional freedoms is nowhere more vital than in the community of American schools." Shelton v. Tucker, supra at 364 U. S. 487. The classroom is peculiarly the "marketplace of ideas." The Nation's future depends upon leaders trained through wide exposure to that robust exchange of ideas which discovers truth "out of a multitude of tongues, [rather] than through any kind of authoritative selection." United States v. Associated Press, 52 F. Supp. 362, 372. In Sweezy v. New Hampshire, 354 U. S. 234, 354 U. S. 250, we said: "The essentiality of freedom in the community of American universities is almost self-evident. No one should underestimate the vital role in a democracy that is played by those who guide and train our youth. To impose any strait jacket upon the intellectual leaders in our colleges and universities would imperil the future of our Nation. No field of education is so thoroughly comprehended by man that new discoveries cannot yet be made. Particularly is that true in the social sciences, where few, if any, principles are accepted as absolutes. Scholarship cannot flourish in an atmosphere of suspicion and distrust. Teachers and students must always remain free to inquire, to study and to evaluate, to gain new maturity and understanding; otherwise our civilization will stagnate and die.""