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The Blue Book of Grammar and Punctuation

What Is the Plural of Thesis?

If you decide to stay in college long enough, you may eventually be required to write a thesis, which is an original academic work that demonstrates the research and critical-thinking skills you’ve developed along the way.

Most graduates have to write only one thesis, but what happens if several students are discussing theirs as a group? How would you refer to more than one thesis?

Let’s establish the proper plural of thesis.

Finding the Plural Version of Thesis

We won’t keep you hanging: The plural of thesis is theses.

Those who are currently working on these documents, or who spend a lot of time in academic settings, might have already known that. But beyond university halls, daily communication can tend to pluralize this word in other ways, such as thesises or thesi.

Although neither alternate spelling is correct, one might understand why people would take such an approach in constructing other plurals of thesis. It follows suit with how we pluralize other similar-sounding English words (e.g., cactus to cacti).

This brings us to our next question.

Why Is Theses the Plural of Thesis?

If the correct pluralization of thesis seems at all odd to you, you aren’t alone. It’s a word many people might not always remember and enunciate. Thesis becomes theses in plural form for two reasons:

1) The word thesis has a Greek root, and theses is how it is pluralized in that original language.

2) There are many English words ending with -is that take on -es endings when pluralized: e.g., crisis becomes crises.

The pluralization isn’t all that unique. However, any confusion can probably be attributed to the relative scarcity of such words in printed or spoken language. You might come across crises if you watch or read the news a lot, but you may not exchange it much in conversation. Likewise, the word theses may rarely appear other than in particular academic contexts.

Continue Practicing Your Writing and Grammar

It’s always valuable to improve your writing and grammar skills, of course, but some areas of American English are more easily learned through absorption and practice than by studying tips. Just as you might run through scales on the guitar or piano, repetition and exposure to certain words and principles will strengthen your comfort and familiarity with them.

If you are one who loves to enhance your precision and eloquence in American English, we encourage you to look through our site regularly and take advantage of the many articles and posts that we offer. Continue reading and learning beyond English grammar as well. Seek knowledge outside of your normal interests or areas of expertise. Take on new information and thoughts.

In addition to rounding your knowledge and viewpoints, your grammar and writing will further develop as well!

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