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Religion and worldview

Carnegie and his family belonged to the Presbyterian Church in the United States of America, also known informally as the Northern Presbyterian Church. In his early life Carnegie was skeptical of Calvinism, and religion as a whole, but reconciled with it later in his life. In his autobiography, Carnegie describes his family as moderate Presbyterian believers, writing that "there was not one orthodox Presbyterian" in his family; various members of his family having somewhat distanced themselves from Calvinism, some of them leaning more towards Swedenborgianism. While a child, his family led vigorous theological and political disputes. His mother avoided the topic of religion. His father left the Presbyterian church after a sermon on infant damnation, while, according to Carnegie, still remaining very religious on his own.

Witnessing sectarianism and strife in 19th century Scotland regarding religion and philosophy, Carnegie kept his distance from organized religion and theism. Carnegie instead preferred to see things through naturalistic and scientific terms stating, "Not only had I got rid of the theology and the supernatural, but I had found the truth of evolution."

Later in life, Carnegie's firm opposition to religion softened. For many years he was a member of Madison Avenue Presbyterian Church, pastored from 1905 to 1926 by Social Gospel exponent Henry Sloane Coffin, while his wife and daughter belonged to the Brick Presbyterian Church. He also prepared (but did not deliver) an address in which he professed a belief in "an Infinite and Eternal Energy from which all things proceed". Records exist of a short period of correspondence around 1912–1913 between Carnegie and 'Abdu'l-Bahá, the eldest son of Bahá'u'lláh, founder of the Baháʼí Faith. In these letters, one of which was published in The New York Times in full text, Carnegie is extolled as a "lover of the world of humanity and one of the founders of Universal Peace".