Each unit should have only limited knowledge about other units: only units “closely” related to the current unit.
Or: Each unit should only talk to its friends; Don’t talk to strangers.

每个模块（unit）只应该了解那些与它关系密切的模块的有限知识（knowledge）。
或者说，每个模块只和自己的朋友“说话”（talk），不和陌生人“说话”（talk）。

Don’t Repeat Yourself

不要重复自己

You Ain’t Gonna Need It

你不会需要它

Keep It Simple and Stupid.
Keep It Short and Simple.
Keep It Simple and Straightforward.

尽量保持简单

High-level modules shouldn’t depend on low-level modules. Both modules should depend on abstractions. 
In addition, abstractions shouldn’t depend on details. Details depend on abstractions.

高层模块（high-level modules）不要依赖低层模块（low-level）。高层模块和低层模块应该通过抽象（abstractions）来互相依赖。
除此之外，抽象（abstractions）不要依赖具体实现细节（details），具体实现细节（details）依赖抽象（abstractions）。

Clients should not be forced to depend upon interfaces that they do not use

客户端不应该被强迫依赖它不需要的接口

Functions that use pointers of references to base classes must be able to use objects of derived classes without knowing it

子类对象（`object of subtype`/`derived class`）能够替换程序中父类对象（`object of base`/`parent class`）出现的任何地方，并且保证原来程序的逻辑行为不变及正确性不被破坏。

software entities (modules, classes, functions, etc.) should be open for extension , but closed for modification

软件实体（模块、类、方法等）应该“对扩展开放、对修改关闭”