Why does Montesquieu believe the legislature and the executive power cannot be one person?

Montesquieu believe the legislature and the executive power cannot be one person so that both do not exhibit too much influence on each other

Explanation:

Montesquieu was a writer who was different from other contemporary writers. The book was a piece of political propaganda written after 20 years of observation. He was the person who believed legislature and executive power should be different and placed the King away from legislature.

He quoted that they have to be independent on each other so that they need not be subordinate to each other but it is also important that they have some interdependence so that they do not destroy essential independence. Montesquieu believed that the two powers should not influence each other and each should have its own responsibilities.