Horace Mann (May 4, 1796 - August 2, 1859) was an American educational reformer and Whig politician dedicated to promoting public education. A central theme of his life was that "it is the law of our nature to desire happiness. This law is not local, but universal; not temporary, but eternal. It is not a law to be proved by exceptions, for it knows no exception."
Secular nature
As the Old Deluder Satan Act and other Massachusetts School Laws attest, early education even under state control in Massachusetts had a clear religious intent. However, by the time of Mann's leadership in education, various developments (including a vibrant populist Protestant faith and increased religious diversity) fostered a secular school system with a religiously passive stance.  While Mann affirmed that "our Public Schools are not Theological Seminaries" and that they were "debarred by law from inculcating the peculiar and distinctive doctrines of any one religious denomination amongst us ... or all that is essential to religion or to salvation," he assured those who objected to this secular nature that "our system earnestly inculcates all Christian morals; it founds its morals on the basis of religion; it welcomes the religion of the Bible; and, in receiving the Bible, it allows it to do what it is allowed to do in no other system--to speak for itself. But here it stops, not because it claims to have compassed all truth; but because it disclaims to act as an umpire between hostile religious opinions."  Mann stated that this position resulted in a near-universal use of the Bible in the schools of Massachusetts and that this served as an argument against the assertion by some that Christianity was excluded from his schools, or that they were anti-Christian.  Mann also once stated that "it may not be easy theoretically, to draw the line between those views of religious truth and of Christian faith which is common to all, and may, therefore, with propriety be inculcated in schools, and those which, being peculiar to individual sects, are therefore by law excluded; still it is believed that no practical difficulty occurs in the conduct of our schools in this regard."  Rather than sanctioning a particular church as was often the norm in many states, the Legislature proscribed books "calculated to favor the tenets of any particular set of Christians.

Q: What is meant by secular nature?
A: Mann affirmed that "our Public Schools are not Theological Seminaries

Q: What are some important aspects of secular nature?
A: debarred by law from inculcating the peculiar and distinctive doctrines of any one religious denomination amongst us
Was Mann well known to a lot of people?
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