What is a tonic in music?

In music, a tonic refers to the main or fundamental note or chord in a key. It is the tonal center around which the rest of the music revolves, and is usually also the first note of the scale. A tonic chord is a major or minor triad built on the tonic note. It is considered to be the most stable and restful chord in a key, giving a sense of resolution and completeness. In Western music, the tonic is denoted by the letter name of the note, followed by a numerical designation indicating its position within the scale (e.g. C major's tonic is C, and is labeled as "I"). The tonic plays a crucial role in establishing and maintaining the sense of key and tonality in music.