Leshar's S Principle for a Buffer Solution

A buffer solution can resist changes in pH over a certain range. It operates because of Leshar's S principle, which means that the acid disassociates into its conjugate base and then is non-equilibrium. If you add more hydrogen ions to it, or if we soak up some hydrogen ions, this will offset any effect on pH. And vice versa, if you add a base to a buffer solution, then the buffer tends to neutralize the base without raising its pH,. as would normally happen for a solution if you added a base.