English grammar is commonly known as one of the harder systems to learn. With strange, archaic rules as well as numerous exceptions to those rules, it makes sense that people tend to ignore the more obscure ones and focus on the day-to-day rules that make regular communication easier. However, when you’re writing to impress, it always helps to have some obscure rules in your back pocket. Listed below are five of the most obscure rules of English grammar.

Compound Subjects

Compound subjects behave weirdly when separated by or and nor. It’s because when a compound subject is separated by an, or, or nor, the verb will agree with the most recent noun. When the noun is singular, the verb is singular. When the noun is plural, the verb is plural.


We’re going back in time here. You was the polite version of thou, and not the other way around. Even though you might think it sounds stuffy now, thou was considered informal and used when you had a degree of familiarity with the other person (like “tu” and “usted” in Spanish). To use thou with someone who was considered higher status, like a king, was disrespectful.

Em Dashes and Hyphens

Em dashes, hyphens, and en dashes are not interchangeable. (Em-dash: — En-dash: – Hyphen: –)
Em-dashes are used as heightened parentheses; if you want to insert a thought into your sentence, em-dashes will work best. For example, “I thought we were friends — more than friends, even!”

En-dashes are used to separate values. For example: “I like about 2–3 people at any given time. You’re not special.” Hyphens are reserved for compound modifiers. For example, “Now, you’re being next-level mean!”

A and An

The articles a and an are used based on vowel sounds, not actual vowels. This is why the phrase “an hour” is grammatically correct while “a hour” is not.

The Subjunctive

The subjunctive mood in general is confusing and obscure, and not something we think about unless we have to. It specifically describes something that is not a known objective fact, like a mood, a wish, or a dream. For example, “If I were to win the lottery, I would never have to work again.”