Abstract: Today a lot of people not only from industrial community but also from academic community simply take As- pect-Oriented Programming (AOP) as modularizing crosscutting concerns and in a narrow-mined way to believe that AOP is just an extension or an effective supplement to Object Oriented Programming (OOP). Based on the definition of AOP, its nature which makes it different from the other programming languages was dug out. And the quantified state- ment and aspect in the definition were formalized. Moreover the semantics of them were defined. And then we argued quantification and obliviousness in the definition are the real nature of AOP. Modularizing crosscutting concerns is just a benefit from it. And AOP is a new programming paradigm which is independent of all the other programming langua- ges. Based on the definition,the minimum condition set which Aspect Oriented Programming Languages (AOPI)need to satisfy was proposed. And the difference between the mainstream AOPL from the view of the definition was probed into.

Key words: Aspect-oriented programming, Aspect-oriented programming language, Crosscutting concerns, Quantification, Obliviousness