During the classical era, composers generally preferred a type of harmony known as tonal harmony. This type of harmony is based on the organization of musical pieces around a central tonic note and chord, which serves as a sort of "home base" for the piece.
In tonal harmony, the tonic chord is typically established at the beginning of a piece and serves as a reference point for the rest of the music. Other chords in the piece are then related to the tonic chord through their distance from it in the scale. For example, a chord that is a perfect fifth above the tonic chord is considered to be closely related to it, while a chord that is a major third above the tonic chord is considered to be more distantly related.
Composers in the classical era often used this system of tonal relationships to create a sense of movement and tension in their music. By moving between closely related and more distantly related chords, they were able to create a sense of tonal pull or tension that ultimately resolved back to the tonic chord. This sense of tension and resolution was an important aspect of classical era music and helped to create a sense of structure and coherence in the music.
In addition to using tonal harmony, classical era composers also often made use of other harmonic techniques such as modulation, which is the process of changing from one key to another within a piece of music. Modulation allows composers to create a sense of contrast and variety within a piece and can be used to create dramatic effects or to bring a sense of closure to a piece.
Overall, classical era composers generally preferred tonal harmony and used it as a means of creating structure, coherence, and a sense of tonal movement in their music. This preference for tonal harmony was an important aspect of classical music and continues to be a significant element in much of the music composed today.