Sometimes a sentence will have what is called a "free modifier" at the end. This is a phrase that refers back to something earlier in the sentence, and it is called a "free modifier" because you can actually move the phrase somewhere else in the sentence without changing the meaning. When you have a free modifier phrase at the end of a sentence, it is set off with a comma.
Here is an example of a
free modifier at the end of a sentence:
- Hercules killed the monstrous hydra, chopping off all nine of its heads.
You can tell that this is a free modifier because you can safely move the phrase somewhere else in the sentence if you want, e.g.
Chopping off all nine of its heads, Hercules killed the monstrous hydra. Meanwhile, without the comma, the sentence would not make sense; it would mean the hydra was killed while it was chopping off its own heads!
Hercules killed the monstrous hydra chopping off all nine of its heads.
Here, on the other hand, is an example of a sentence where the modifier is not free, which means you do not use a comma:
- Hercules saw the monstrous hydra swimming beneath the surface of Lake Lerna.
If you did include a comma, the sentence would not make sense. Instead, it would mean Hercules was the one who was swimming beneath the surface of the lake, not the hydra:
Hercules saw the monstrous hydra, swimming beneath the surface of Lake Lerna.
For more information about commas, see
Purdue's OWL.
Visit
Wikipedia for more information about Hercules and the Hydra. In this image, you can also see the crab attacking Hercules from behind, too!
