Here's why:
* No rhyme scheme: The poem doesn't follow any regular rhyme pattern.
* Irregular meter: It doesn't adhere to a consistent metrical structure like iambic pentameter (the most common meter in blank verse).
* Emphasis on imagery and rhythm: Sandburg uses vivid imagery and an irregular, flowing rhythm to create a sense of the fog's movement and presence.
Blank verse is characterized by its unrhymed iambic pentameter. While "The Fog" uses a flowing rhythm, it doesn't follow the strict structure of blank verse.