OPA1652 INPUT COMMON MODE VOLTAGE RANGE

I need some help understanding input common mode voltage range.  As a basis for the discussion lets start with a OPA1652.  Vcm for this device is stated in the data sheet as:

   VCM Common-mode voltage range (V–) + 0.5 (V+) – 2

Please describe what the maximum input voltage can be and how Vcm effects it. 

Thanks,

John