Critical opinion of the poem began to shift in the middle of the 20th century. In 1980, Whitman's biographer Justin Kaplan called the poem "thoroughly conventional". The literary critic F. O. Matthiessen criticized the poem, writing in 1941 that its early popularity was an "ample and ironic comment" on how Whitman's more authentic poetry could not reach a wide audience. Michael C. Cohen, a literature professor, said Matthiessen's writing exemplified 20th-century opinion on the poem. In the 1997 book A Reader's Guide to Walt Whitman, scholar Gay Wilson Allen concluded that the poem's symbols were "trite", the rhythm "artificial", and the rhymes "erratic".