I've encountered this sentence, but I can't understand what is the function of for in it. Also, what is the subject for ... is to understand ...

But it is worth trying, for to understand the initial shock of those images is to understand the extraordinary power and magic of cinema, the unique, hypnotic quality that has made film the most dynamic, effective art form of the 20th century.

  • Its function depends on which grammar you subscribe to: some people treat it as a subordinator in which case its function is marker of the subordinate clause it introduces; others (including me) treat it as a preposition, in which case its function is head of the preposition phrase. Either way the meaning is similar to "because" or "as".
    – BillJ
    Commented Feb 23, 2017 at 14:14

2 Answers 2


As Erin pointed out, in this context for is a conjunction meaning because.

There is a 1958 song by the Teddy Bears called "to know him is to love him". This gives a clue how to read the ...is to understand... section.

to understand X is to understand Y

What this means is that if you get to a point where you understand X, you will be also able to understand Y.


In this example for is being used as a conjunction like because or since.

Here is a website with some examples: Using “For” to Mean “Because”

  • Can you also explain what is the subject for "is to understand ..."?
    – Sam
    Commented Feb 23, 2017 at 14:07
  • @Sam the non-finite clause is to understand ... is subjectless, as is typical of non-finite clauses. We understand the subject to be some arbitrary persons.
    – BillJ
    Commented Feb 23, 2017 at 14:33
  • @BillJ: don't forget the is. To get down and dirty, you should say that is to understand... is a verb + subject complement (ok, it's a verb + subjectless subject complement if you want to be pedantic), and its subject is to understand the initial shock.... Call that a subjectless subject if you will.
    – JavaLatte
    Commented Feb 23, 2017 at 14:53
  • 1
    Sorry, I was being sloppy. I should have said to understand the extraordinary... (not is to understand ...). The subject clause and the complement clause are both subjectless non-finites (though both subjects are understood as the same arbitrary persons). We understand: for x to understand y is for x to understand z.
    – BillJ
    Commented Feb 23, 2017 at 15:27

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