How does a spondee differ from the common English metrical feet?

In English prosody, the spondee differs from common metrical feet primarily in its function and composition. While common feet like the iamb, trochee, anapest, and dactyl serve as the building blocks that determine a poem's metre, the spondee never functions as a determinant of a metrical pattern.123

Instead, the spondee—defined as a foot consisting of two stressed syllables—occurs only as a substitution for other, more standard feet. Furthermore, while common feet rely on a specific arrangement of stressed and unstressed syllables, the spondee is difficult to achieve in English because there are virtually no words where two syllables receive truly equal stress. Consequently, in English verse, a spondaic foot is typically composed of two separate monosyllables, such as "He who".132