Tutoring English, one might encounter this elegant topic about writing style.

A complex sentence is one that joins two thoughts by subordinating one to another – that is, the idea that gives extra information, but does not contain the central action, is written to be dependent on the “main” idea. Here’s an example:

Although they had to clear a foot of snow from the driveway before leaving, they drove off within fifteen minutes.

In the sentence above, the subordinate part is underlined. The fact that they had to clear snow from the driveway before leaving is interesting information, but the central action is that they drove off. Although is a subordinating conjunction; its presence in the first part of the sentence shows that part to depend on the second part.

According to some English style guides, faulty subordination means that one part of a sentence is constructed to depend on the other, when in fact it doesn’t. Here’s an example:

While he pursued law, his sister studied dentistry.

In the above sentence, the earlier idea doesn’t depend on the latter; the two events happen separately. However, the word while is a subordinating conjunction, so its presence in the first part of the sentence suggests dependence on (aka subordination to) the second part.

The recommended fix for the sentence above might be to join the two ideas with a semicolon, so that each is independent:

He pursued law; concurrently, his sister studied dentistry.

Source:

Hodges, John C. et al. Harbrace Handbook for Canadians, sixth ed. Scarborough: Nelson Education Ltd, 2003.

Shaw, Harry. Handbook of English, fourth Canadian ed. Toronto: McGraw-Hill Ryerson Limited, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.