This is a bit of a trick question! There isn't really a single pair of words that perfectly encapsulates the essence of science. However, two important words often associated with the scientific process are:

* "Why?" Science is driven by curiosity, a constant desire to understand the "why" behind things.

* "Evidence". Science relies on evidence to support its claims.

So, while there isn't a single "most important" pair, "why" and "evidence" represent key aspects of the scientific approach.