gmatsamurai wrote:Hey Guys,
I am studying from OG for SC. I am on the parallelism topic and I have come across this:
The only way to know is to take the plunge. - Correct
The only way to know is taking the plunge. - Incorrect.

No issues I understand this. But how about:
The only way to know is by taking the plunge. Is this incorrect because this sounds correct to me but somehow, in my head, I can't reason it out.

when u have to show the intention then you are supposed to use infinitives like to

I love your question and think that there are a couple of practical notes that can help:

1) On the GMAT, you won't be asked to fix an error without choices, so you don't necessarily need to recognize that the second sentence is **wrong**, just that it's **different** from the first, and that a decision is required. You're not editing a manuscript - the beauty of GMAT SC is that you can make your decisions based on differences and not by having to read each sentence with an eagle eye for this stuff.

2) When you see this difference, you can then examine it to figure out why one has a problem. Here, one way to look at it is this - the sentence could be interpreted two ways:

The way to X is to Y

or

X is Y-ing, where "The only way to know" is the subject of the verb "taking"

And the second interpretation is illogical and awkward. So the "correct" example you gave, by fixing that potential problem, is correct.

Honestly, that's not a problem that I would notice without a comparison sentence - but on the GMAT you always get that comparison between answer choices to help alert you to that 'wait a second...that actually does have a problem" subtle error. When you can see that you're forced to make a decision, you can further investigate to see those problems.