Co-ordinating units of writing must all be of the same grammatical kind. This is what is referred to as preserving parallel structure. For instance, nouns must match with nouns, adjectives with ...

As you can see, faulty parallelism--or a breakdown in parallel structure--happens when a pair or series of co-ordinating units (nouns, adjectives, adverbs, etc.) are not of the same kind. In number 1, ...