What alteration is made to create a minor interval from a major interval?

To create a minor interval from a major interval, the interval is lowered by a half step. This change alters the specific distance between the two notes and is the defining characteristic of minor intervals. For example, a major third interval (which consists of four half steps) becomes a minor third interval (which consists of three half steps) when one of the notes is lowered by a half step.

This adjustment is critical in music theory as it delineates the difference between major and minor tonalities, which are foundational elements in composition and performance. Understanding this concept is essential for any musician, as it underpins the emotional qualities of music, where minor intervals often evoke a more somber or introspective mood compared to their major counterparts.