Can a primary chord harmonize every note of melody in major key?

In general, a single primary chord cannot harmonize every note of a melody in a major key. While major primary chords (I, IV, and V) can create functional harmony, they may not provide the most appropriate or colorful harmonization for each melody note.

Here are the specific notes and why certain primary chords may not harmonize well:

1. Root (Do): The I chord (tonic) harmonizes well with the root (Do).

2. Second (Re): While the IV chord (subdominant) can sometimes work, it may sound weak or incomplete, especially if the melody note emphasizes the leading tone tendency.

3. Third (Mi): The I chord (tonic) provides the strongest harmonization for the third (Mi).

4. Fourth (Fa): Both the I chord (tonic) and the V chord (dominant) can harmonize the fourth (Fa), depending on the context.

5. Fifth (Sol): The V chord (dominant) provides the strongest harmonization for the fifth (Sol).

6. Sixth (La): The I chord (tonic) and the VI chord (submediant) can both work, but the VI chord may provide a more colorful or unexpected sound.

7. Seventh (Ti): The V chord (dominant) provides the strongest harmonization for the seventh (Ti).

However, it's important to remember that music theory is flexible, and there may be exceptions or instances where a primary chord can harmonize a note effectively, depending on the musical context and composer's intent. Therefore, it's always best to experiment and use harmonic principles in a creative way to achieve the desired musical效果。