Correlative conjunctions should be followed by grammatical structures of the same kind. Correlative conjunctions have two parts. Examples are: both…and…, not…but…, not only…but also…, either…or, neither…nor… etc.
Incorrect: It was both a long journey and tedious.
Correct: The journey was both long and tedious.
Incorrect: Either you must confess your involvement or prove your innocence.
Correct: You must either confess your involvement or prove your innocence.
Incorrect: The measure is both unjust and it is unconstitutional.
Correct: The measure is both unjust and unconstitutional.
When you make comparisons, the things that you compare should be in parallel structures.
Incorrect: My salary is smaller than a sweeper.
Your salary can’t be smaller than a sweeper, but it can be smaller than that of a sweeper.
Correct: My salary is smaller than a sweeper’s.
Correct: My salary is smaller than that of a sweeper.
Incorrect: His teaching was like Jesus.
Correct: His teaching was like that of Jesus.
If an article applies to all the items in a series, it needs to be used only before the first item in the series. Or you can use it before all the items in the list.
Incorrect: I ate an apple, orange and a banana.
Correct: I ate an apple, an orange and a banana.
Incorrect: I bought a camera, stereo and a mobile phone.
Correct: I bought a camera, a stereo and a mobile phone.
Correct: I bought a camera, stereo and mobile phone.