As we learned in the previous two lessons on scale structure, both the Number System and Solfege can be used to describe the very same musical stuff…
Here are both systems used to describe the C Major Scale…

By the way, Do=1, Re=2, Mi=3, Fa=4, So=5, La =6, and Ti =7… always, no matter what key you are in!

Which begs one to ask…
- Why two systems and not just one?
- Which system should I learn?
And the answer is: You should learn both systems, for at least five reasons…
- Both systems are widely-used in music theory to describe, communicate, and analyze musical patterns such as scales, melodies, and chord progressions.
- Neither system is perfect. Each has its pros and cons, capabilities and limitations.
- Both conventions will be used throughout the Piano-ology website as appropriate.
- The Number System is better-suited for describing chord structure (independent of tonality), as you will see when you study chords.
- Solfege is better-suited for analyzing and doing ear training for scales and melodies.