[2] After serving in the army in 1918, he traveled in Europe for a year with his friend, Mark Van Doren.

There he challenged then-fashionable notions of scientific progress and optimism, arguing that science leads logically to a bleak view of the human condition.

[3]: 319  In the 1940s he wrote widely read biographies of Samuel Johnson and Henry David Thoreau and—largely inspired by Thoreau—published his first nature book, The Twelve Seasons (1949).

[7] Historian Donald Worster commented that Krutch "became a kind of pantheist or ethical mystic, caught up in the joy of belonging to something greater than one's self.

"[8] His brother, Charles Krutch, was the renowned Tennessee Valley Authority (TVA) photographer.