A friend and his son visited an aquarium recently and came home with a grammar question: Is fishes correct?
Language is an amazingly efficient communication tool. Often a single well-chosen word can convey a wealth of information. Fishes is a good example, telling you that a person is talking about several species grouped together.
If you have a tank of goldfish, you would say, “I fed my fish this morning.” But if you have blue gouramis, blind cavefish, and zebra fish (as we once did), you would say, “I fed my fishes this morning.”
It’s the same with deer. My younger sister often sees white-tailed deer in the back yard of her rural Massachusetts home. But if she lived in, say, Montana, she might see both white-tailed deer and mule deer in her back yard. In that case (being my sister and therefore a person who takes usage seriously), she would say, “I saw several deers today.”
This usage explains why you sometimes hear or read the word peoples. When you’re grouping human beings together, they’re simply called people:
Many people in the United States worry about global warming.
But when you’re talking about several ethnic groups, use peoples:
Anthropologists study the peoples of the world.
King George VI used people this way in a famous remark he made during World War II. Someone in a cheering crowd called out to him, “Thank God for a good King.” His reply, “Thank God for a good people,” shows that he could have been an excellent English teacher as well as a very effective king. Good for him.