The acidity or basicity of a compound is controlled by several structural factors....this gives a way to rationalise the acidity and potentially predict the relative acidity of different molecules or functional groups within a molecule.

Basis : for basicity, look for factors that affect the availabilty of the electrons in the conjugate base, A-

Using the Lewis definition of a base (an electron pair donor), if the electrons in A-, are less available, there will be less reaction with the proton to give the parent acid, H-A, hence a weaker base.

The structural factors affecting basicity are the same as those affecting acidity, we just have to apply them the opposite way around because we are looking at the opposite reaction.

Summary of structural factors: