Introductory "it"

Introductory ‘ It ’

A. To understand this lesson is easy . B.  It is easy to understand this lesson .

In this pattern , it has no meaning . It is used only to fill the subject position in the sentence . Thus , it is called introductory “ it ” .

A & B mean the same thing , but sentence B is more common and useful than A . A was introduce mainly to make the meaning of C easier to understand .

Introductory “ it ” can fill the position both of the subject &  object .

Introductory “ it ” as a subject :

To watch musical programs is pleasant .

It is pleasant to watch musical program .

To play football must be fun .

It is fun to play football .