1. If you can express the language as a regular expression then the language is Regular

eg: $a^{n},n \geq 0$ is a regular language.

2. If you can recognize the language with a stack machine (Push Down automata), then it is a context free language.

eg $a^{n}b^{n},n \geq 0$ is a context free language.

3. If you can recognize the language with a Linear bound automaton (Turing machine with a finite tape), then its a context sensitive language.

4. If you cannot construct any of the above , then it belong to Phase structured language.

Turing machine can be constructed for recognizing any recursively enumerable language.