A lot of seemingly arbitrary or idiomatic grammar rules are, in fact, based on logical principles. When you know the principles underlying grammar rules, the rules will be much easier to understand and apply. One of the most fundamental principles is consistency. Different parts of a sentence need to be consistent with each other in various aspects. This allows readers to relate different parts of a　sentence and follow the flow of ideas smoothly. For example, subject and verb should be consistent in number. When the subject is plural, the verb should also be plural. Another example is that singular female pronoun (she/her) should be used to replace a female name.

7. Unparallel structure

When related ideas are placed together in a sentence, they should be expressed in the same (i.e. consistent) grammatical form in parallel structure. The second sentence below is so much easier to follow because various phrases are constructed in consistent grammatical forms and parallel sentence structures.

•  A big basket of sweet sun-yellow corns was laid in front of the house while a flock of hungry pigeons, at the back of it, was trapped.

•  In front of the house laid a basket of sweet corns while at the back of it trapped a flock of hungry pigeons.

7a. Illogical comparison

Two items can only be properly compared when they are parallel. At the first glance, the sentences below make sense since your brain automatically sorts out the odds for you and figures out what the sentences really meant. However, what the sentences literally say are illogical.

7b. Inappropriate placement and wording of parallel information in correlative constructions

The following correlative conjunctions connect related ideas. In last week’s article, I have mentioned that they must appear in pair. According to the principle of consistency, the ideas these pairs connect should be expressed in the same grammatical form.

• both…and
• between…and
• either…or
• neither…nor
• not only…but also
• whether…or

8. Incorrect comparative structure (e.g. “more busier”)

Comparative form (more/less/-er) shows the difference between two (groups of) objects while superlative form (the most/least/-est) shows the difference between three or more (groups of) objects. We can only tell exactly which item has more of a certain quality than the other one when there are two objects being compared. And it is only necessary to say something has the most of a certain quality when there are three or more objects. For example, Daniel is taller than Mary. He is actually the tallest in the class.

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(Next Tue: Identifying Sentence Errors cont'd)