Question

If base criteria is not given then recursive function will

Answer 1

Recursion has something to do with infinity. I know recursion has something to do with infinity. I think I know recursion has something to do with infinity. He is sure I think I know recursion has something to do with infinity. We doubt he is sure I think I know ... We think that you think that we convinced you now that we can go on forever with this example of a recursion from natural language. Recursion is not only a fundamental feature of natural language, but of the human cognitive capacity. Our way of thinking is based on a recursive thinking processes. Even with a very simple grammar, like "An English sentence contains a subject and a predicate, and a predicate contains a verb, an object and a complement", we can demonstrate the infinite possibilities of the natural language. The cognitive scientist and linguist Stephen Pinker phrases it like this: "With a few thousand nouns that can fill the subject slot and a few thousand verbs that can fill the predicate slot, one already has several million ways to open a sentence. The possible combinations quickly multiply out to unimaginably large numbers. Indeed, the repertoire of sentences is theoretically infinite, because the rules of language use a trick called recursion. A recursive rule allows a phrase to contain an example of itself, as in She thinks that he thinks that they think that he knows and so on, ad infinitum. And if the number of sentences is infinite, the number of possible thoughts and intentions is infinite too, because virtually every sentence expresses a different thought or intention."1 

We have to stop our short excursion to the use of recursion in natural language to come back to recursion in computer science and programs and finally to recursion in the programming language Python. 

The adjective "recursive" originates from the Latin verb "recurrere", which means "to run back". And this is what a recursive definition or a recursive function does: It is "running back" or returning to itself. Most people who have done some mathematics, computer science or read a book about programming will have encountered the factorial, which is defined in mathematical terms as 

n! = n * (n-1)!, if n > 1 and 0! = 1 

It's used so often as an example for recursion because of its simplicity and clarity. We will come back to it in the following.