A Bangor University expert believes the constant battle for prominence between words like "cat" and "dog" could help to explain.
Dr Gary Oppenheim, of the university's Language Production Lab, is working to reveal the "algorithms and architectures" behind vocabulary.
So he has built a computer system which aims to mimic human word production and "learns as it speaks".
"Often, we're producing two or three words per second and speaking about 15,000 words in a given day, which is pretty amazing.
Dr Oppenheim, originally from Detroit, Michigan, argues the mind retrieves words by activating their "semantic features" - the elements that make up their meaning.
Some words share a number of features - for instance, the words "dog" and "cat" are both furry, quadrupeds, with a tail that are domesticated.
He argues such words, linked by their shared semantic features, are constantly reorganised and refined based on their usefulness in the recent past. »