Irregular plurals?

So tell me is it formulas or formulae? Sheep or sheeps? Kine or cows? Agenda or agendas? What is with all these weird plurals?

Formulae is the original plural but it seems that people are using the regular plural formulas more. Why is this?

It seems strange that some plurals follow the rule of –ies –es or -s as their endings but some stay the same (sheep) or change the vowels (feet) or change totally (kine). Following this on the internet I found out a lot of useful information that I decided to follow to see whether they do follow a rule or whether they are totally different.

The most useful source I found was en.wikipedia.org/wiki/Regularization_(linguistics)as it explained where the irregular plurals came from and why they were different to regular plurals. It explained that some plurals don't change because they are proper nouns. It also explained that foreign words that are borrowed from other countries are normally exceptions to the rule. It said that some words are so commonly used that the plural becomes the singular word for example agendum is the singular word and agenda is the plural but this is used so often that there has been a new plural for agenda making it agendas.

However when I Googled irregular plurals most websites didn't explain why these were like this it was more about teaching children what the plurals were.

One link on Wikipedia under linguistic regularization took me to a link for a book search (essential introductory linguistics by Grover Hudson) which explained why there are often two ways to say the plural for example the plural of cow is kine but also cows. This book said that children often want to follow the rules so when they do not know the plural of the word the irregular ending is not used and so it becomes a regular plural like cows.

On another website it explained this further by saying that these irregular plurals become more commonly regular the more they are used. This is because we do not know what the plural is and so we automatically follow the rules. This leads to having two plurals such as formulas and formulae. The irregular plural then dies out leaving us with a plural that follows the rules such as cows. It then explained that the less frequent a plural is used the faster it becomes regularised.

After reading the explanations on Wikipedia about how irregular plurals work in their original origin it seems they are actually rules that they follow just not the English rule. This would be interesting to follow to see if this is a rule where they originated or if they are irregular in other countries as well.

By Kirsty Burnett.