I am having some difficulty in understanding the reason for the various types of acids/bases, of which i refer to bronsted-lowry, arrehenius, and lewis acids/bases. A bronsted acid donates an H+ and a bronsted base accepts a H+. However, a lewis accept acceps an e- pair and a lewis base donates an e- pair. This seems contradictory, is a lewis acid a bronsted base and lewis base a bronsted acid? What is the purpose of this, why isnt there a single definition of an acid and base.