Just like “Whether” versus “If,” the GMAT likes to use “as” and “like” in special, specific ways:
“Like” is used to compare two things.
CORRECT: Josh’s hair color is just like his mother’s.
Here we are comparing two hair colors. It would be awkward and incorrect to try and use “as” in that sentence.
INCORRECT: Josh’s hair color is just as his mother’s.
“As” is used to link two ideas together.
CORRECT: Just as yoga is a form of low-impact exercise, pilates is easy on the joints.
Here we are comparing the entire idea of yoga as a type of exercise to the idea that pilates is similar. You will use “as” when the ideas you are comparing include a verb.
Remember also that “as” is one of our FANBOYS:
Conjunctions and Prepositions
That means it’s a conjunction. “Like” is a preposition. It makes sense that you wouldn’t use these parts of speech in the same way.
A conjunction is a linking word between the difference clauses of a sentence. A clause is a phrase that contains a noun. A preposition describes position, so use “like” before nouns (which we call the object of the preposition). The meaning of “like” is similar to “for example.”
CORRECT: He felt like his head was the size of a balloon.
CORRECT: Michelle was as annoyed by the customer service as she was by the tasteless entrée.
Look out for questions on the GMAT where “like” is being used as a conjunction and not as the true preposition it is. “Like” has become much more common in the last several decades, so you can’t necessarily trust your ear to recognize this error. Something to think about next time you hear someone use these words in casual conversation! “It’s like, you know….”