146. The primary forms are built up by combining two or more periods.
The small two-part primary form (often called song-form or Lied-form) consists of two periods so placed that the second constitutes a consequent or antithesis to the first. The second half of this second period is often exactly the same as the second half of the first period, thus binding the two periods together into absolute unity. The theme of the choral movement of the Ninth Symphony (Beethoven) quoted below is a perfect example of this form. Other examples are "Drink to Me Only With Thine Eyes," and "The Last Rose of Summer."
The small three-part primary form is like the two-part primary form except that it has a section of contrasting material interpolated between the two periods. This middle part is usually an eight-measure phrase.