The most reasonable conclusion based on the excerpts from the poems is:
Donne and Whitman use different diction due to their historical contexts.
This conclusion is supported by the differing styles and themes presented in the excerpts. John Donne's language reflects a more formal and metaphysical style typical of the 17th century, engaging in a direct confrontation with death. In contrast, Walt Whitman's language is more modern, conversational, and rooted in a connection to nature and the cycle of life and death. The distinct diction and themes they use highlight their respective historical contexts.