The 5⁷ of 4 harmony

Roman numeral code: V⁷ / IV
Scale notes: 1, 3, 5, b7
Mode: major
Attributes: impelling forward

The transition from 1 to 4 is made more dramatic by interposing 5⁷ of 4:

       1 -> 5⁷ of 4 -> 4

This sequence solidly establishes the 4 because 5⁷ of 4 strongly anticipates and leads into 4.

5⁷ of 4 is actually the same chord as 1⁷, which is 1 with flatted note 7 added (for example, B flat in the key of C). While this note does not belong to the key of 1, it does belong to the key of 4.