Do, Re, Mi, Fa, Sol, La, Ti, Do' iis known in music as the tonic solfa notation. Solfa or solfge as we know it was first seen in Europe in the 11th century, developed by Guido d'Arezzo, a music theorist and a monk of the Benedictine order who is credited with inventing modern staff notation. 

The mnemonic "Do, Re, Mi, Fa, Sol, La, Ti, Do" serves as a familiar guide to the musical scale and is known in music as the tonic solfa notation. This system, also referred to as solfège, plays a fundamental role in music education and vocal training. The use of solfège facilitates the understanding and internalization of pitch relationships, aiding musicians in developing their musical ear.

The origins of solfège can be traced back to Guido d'Arezzo, a notable music theorist and Benedictine monk. Guido d'Arezzo lived in the 11th century and is credited with revolutionizing musical notation. Prior to his innovations, musical notation was limited, and musicians relied on oral tradition for passing down melodies and harmonies.

Guido d'Arezzo's key contributions include:

1. **Ut-Re-Mi:** Guido d'Arezzo introduced the first syllables of the solfège system as "Ut," "Re," "Mi," "Fa," and so on. These syllables corresponded to specific notes in the musical scale.

2. **Hexachord System:** Guido expanded the traditional diatonic scale to include six notes, forming what he called hexachords. This system provided a more comprehensive framework for teaching and understanding music.

3. **Staff Notation:** Perhaps Guido d'Arezzo's most enduring contribution was the development of modern staff notation. He introduced a set of lines and spaces to represent different pitches, allowing for a more precise and standardized way of notating music.

4. **Ut Re Mi Mass:** Guido d'Arezzo composed a hymn known as the "Ut Re Mi Mass," which served as an instructional tool for teaching his solfège system. The hymn utilized the syllables of solfège to guide singers through the musical scale.

Guido's innovations laid the foundation for the musical notation systems used today. The widespread adoption of solfège in music education reflects its effectiveness in teaching pitch relationships and vocal training. The enduring legacy of "Do, Re, Mi" extends beyond its use in the iconic song from "The Sound of Music" to its roots in the transformative work of Guido d'Arezzo, a visionary figure in the history of music theory.