In addition to his writings on marine life, Ricketts wrote three philosophical essays; he continued to revise them over the years, integrating new ideas in response to feedback from Campbell, Miller, and other friends. The first essay lays out his idea of "nonteleological thinking" – a way of viewing things as they are, rather than seeking explanations for them. In his second essay, "The Spiritual Morphology of Poetry," he proposed four progressive classes of poetry, from naive to transcendent, and assigned famous poets from Keats to Whitman to these categories. The third essay, "The Philosophy of 'Breaking Through'," explores transcendence throughout the arts and describes his own moments of 'breaking through', such as his first hearing of "Madame Butterfly".