While doing push-ups on the beach, the sun shone brightly.
The above sentence may seem okay at first glance, but it contains a dangling modifier, a word or phrase that modifies something it’s not supposed to. In English, introductory phrases like ‘While reading a book on the beach’ modify the noun, or noun phrase, that next appears in the sentence, which in this case is ‘the sun’, so technically, this sentence is saying that the sun was doing push-ups on the beach. No-one would read it to mean that, which is why danglers are forgivable in informal writing, but being a careful writer means being aware of conventions, even if only to avoid the ire of grammar sticklers.
Dangling introductory phrases can be fixed in a number of ways. In this case, the job can be done with something like ‘While I was doing push-ups on the beach, the sun shone brightly’ or ‘While doing push-ups on the beach, I noticed the sun shine brightly’.
Danglers aren’t just found at the beginnings of sentences. Take this one:
‘He was staring at the man by the vending machine wearing dark glasses.’
Rarely do vending machines wear dark glasses.
Here’s a fix: ‘He was staring at the man wearing dark glasses by the vending machine.’