Philosopher Bertrand Russell in his 1957 essay “The Value of Free Thought” wrote
What makes a freethinker is not his beliefs but the way in which he holds them. If he holds them because his elders told him they were true when he was young, or if he holds them because if he did not he would be unhappy, his thought is not free; but if he holds them because, after careful thought he finds a balance of evidence in their favor, then his thought is free, however odd his conclusions may seem.
Fred Edwords, former executive of the American Humanist Association, suggests that by Russell’s definition, even liberal religionists who have challenged established orthodoxies might be considered freethinkers.
In the 18th and 19th century, many thinkers regarded as freethinkers were deists, arguing that the nature of God can only be known from a study of nature rather than from religious revelation. In the 18th century, “deism” was as much of a ‘dirty word’ as “atheism”, and deists were often stigmatized as either atheists or at least as freethinkers by their Christian opponents. Deists today regard themselves as freethinkers, but are now arguably less prominent in the freethought movement than atheists.