1	2	3
S	Single Responsibility	"There should never be more than one reason for a class to change."
O	Open-Closed	"Software entities ... should be open for extension, but closed for modification."
L	Liskov Substitution	"Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it."
I	Interface Segregation	Clients should not be forced to depend upon interfaces that they do not use."
D	Dependency Inversion	"Depend upon abstractions, [not] concretions."