The Aalaapana is an example of a musical form giving scope for improvisation within a framework. It is not totally unstructured or a mere combination of random notes of the raagam, but an emotionally satisfying development of the raagam mood within its definitions but giving scope for creativity. The Aalaapana does not have a rhythmic pattern, but there is an inherent time sense in the phrases. It could take as little as a minute or two or could be expanded to cover even an hour! When made elaborate, aalaapana is usually structured starting at the lower pitches and progressively touching higher pitches and finally covering some quick phrases. In older schools, the aalaapana was supposed to stress more on the melodic aspects of the Krithi to follow and a full exposition of the raagam was reserved to Raagam, Thaanam, Pallavi.
Kalpana Swaram is the extempore singing of solfa (sa ri ga ma etc.) at the end of a krithi or in the middle, taking either the pallavi or other line as a refrain. Rhythmic pattern is the main highlight of kalpana swaram. Each group has to end correctly at the point in the thaalam cycle where the refrain starts. Starting with groups of swarams covering one or two aavarthams, the artiste goes on to larger number of aavarthams often using clever rhythmic patterns at the end of each group before repeating the refrain. The "iruthi makutam" or last group of phrases usually a combination of groups of odd number of notes repeated thrice to correctly coincide with the start of the refrain, has now become a standard practice.
Thaanam is the extempore elaboration of the raagam mood to stress the ghana aspect using the syllables "a, tha, nom, tham". (Historically the term had a different meaning implying skipping of notes.) There is inherent rhythm in thaanam and sometimes artistes have mridhangam accompany the Thaanam though it is not set to any thaalam in particular. One of the definitions of a "ghana" raagam is a raagam which is well suited for thaanam. The present Thaanam form perhaps developed on the Veena which is very suited for it and Thaanam is often played on the Veena after aalaapana before a krithi but vocalists generally reserve it to "raagam, thaanam, pallavi". Some 'chittai' thaanam's (ready made) are available in the ghana panchaka raagams.
Pallavi is the form where instead of a krithi a single line of lyric covering one aavartham (or more if chaapu thaalam is chosen) in 2 kalai or even 4 kalai is taken up for elaboration with great emphasis on the rhythmic aspect. The line could be the pallavi of a well known song (but could be in a different thaalam). Usually sung after aalaapana and thaanam, the pallavi is elaborated in different kaalams including a thisra nadai in which 3 cycles of the pallavi cover 2 aavarthams. Kalpana Swaram invariably follows the pallavi and often the swarams are sung in other raagams returning to the main raagam at the end. In days of 3 or 4 hour concerts raagam, thaanam, pallavi was always included in the concert.