Cetasikas arise along with citta and help in the process of recognizing an object. Several different cetasikas may arise with the citta, and it is the cetasikas that distinguish one type of citta from another. If the citta arises with unwholesome cetasikas, the citta becomes unwholesome. If the citta arises with beautiful cetasikas, the citta becomes beautiful.
There are 52 different cetasikas, divided into three groups according to their character: ethically variable, unwholesome and beautiful.
The ethically variable cetasikas are so called because they can be either wholesome or unwholesome depending on which other cetasikas arise with them. If the other cetasikas are wholesome, a variable cetasika becomes wholesome. If the other cetasikas are unwholesome, a variable cetasika becomes unwholesome.
The definition of a cetasika is that it meets four specific criteria - otherwise it is not a cetasika. This definition pinpoints the relationship between the citta and its attendant cetasikas. Same time, same object, same base.