the only way is if~
I have never gotten to listen to one of those Parental Warning CDs, because Mom and Dad never let me buy them at the mall. So I realized the only way I was gonna get a chance to listen to Rodrick's CD was if I snuck it out of the house. (from Diary of a Wimpy Kid by Jeff Kinney)
The only way I was gonna get a chance to listen to Rodrick's CD was if I snuck it out of the house.
The use of "if" above is grammatical and correct? As far as I know, "If" has two uses.
- used in conditional clauses as adverbial clauses
- used in interrogative clauses as nominal clauses(in this case, if the clause is used as an object, "if" can be replaced by "whether". More importantly, "if" clause cannot be in a 'subject complement' position)
I am confused about which category the "if" above falls under. 1) or 2) or nothing? The "if" clause above is a nominal clause, but at the same time, has a conditional meaning. Also, it is in a subject complement position.
Is this use of "if" grammatical? correct? idiomatic? or just colloquial and informal?
Solution 1:
This construction is fairly common in print. Some examples appear to be formal writing, and I see nothing wrong with them:
But how can all of 5.1-5.5 be true? The only way is if the following is also true: Commonsense Consequentialism (2011) p.130
The only way this will find concrete, tangible, and long-term expression in society and community—in our world—is if you learn how to work with others and form a society—a guild, a school, a hospital... Institutional Intelligence (2017) p.6-7.
In the first example, one could say ...is by accepting the following as true, but the point may be that the "following" is not true (and 5.1-5.5 are not all true as a consequence). The if construction does a better job in that case.
In the second example, one could replace ...is if you learn how ... with ...is by learning how or ...is to learn how... But they are not exactly the same -- the conditionality feels weaker.
The only way the party will be a success is if Susan comes can't be transformed with ...to have Susan come or ....by having Susan come. They both imply Susan hasn't been invited. ...to ensure/by ensuring Susan comes do imply she's been invited, but they also have a different meaning.
Solution 2:
As others have said, the construction is perfectly acceptable English. Grammatically, the if clause in your case is a preposition phrase (PP).
Discussion
While CGEL doesn't explicitly treat this very construction, some things it does say are highly relevant.
The most important takeaway from CGEL is the following: except in cases where it is interchangeable with whether, the word if is a preposition and it functions as the head of a preposition phrase. From p. 600:
We therefore include in the preposition category all of the subordinating conjunctions of traditional grammar, with three exceptions. The exceptions are, first, whether; second, those occurrences of if that are equivalent to whether (as in Ask him if he minds); and, third, that when it introduces a subordinate clause. These items we take to be markers of subordination, not heads of the constructions in which they figure: see Ch. 11, §8.1, for detailed discussion of this issue.
This is one of the more significant differences between CGEL and traditional grammar; its defense in CGEL runs on several pages.
Once it is accepted, however, the grammar of your sentence becomes less mysterious.
Preposition phrases routinely function as complements of the verb be. Probably the most frequent case is that of location complements, as in
[1] The letter is on the table.
More relevantly, we have
The only way is over the plain or along the shore. (source)
The only way is by setting an example. (from COCA)
The only way is by boat. (source)
Conversely, note that some other noun phrases also licence if PP complements (all examples are from COCA):
The only danger we have is if they manage to produce our energy weapons and make them more powerful.
The only explanation that would justify it, in my eyes, is if there's a billion dollars hidden in that painting.
The worst cost is if you're perceived as covering something up.
In conclusion: the construction the only way+be licenses a variety of PP complements, including if-phrases.