All meditative practice can be categorized as one or the other of these disciplines.
Asanga defined tranquility as “Close contraction or binding of the mind, tranquility, unification, and composure.”
The qualities he associated with insight are inquiry,search, complete thought, and investigation of mind and mental activities. “By the power of calm, thought becomes unshakeable in relation to its own object, like a lamp in still air. By the power of insight, the light of right knowledge arises as a result of understanding the reality of dharmas as they are. All obstructions are thereby removed, just as darkness is removed by the appearance of light.” -Kamalasila, heart-student of Khenpo Santarakshita