Learn English – how much, how many, what percent

I would say the best fit is are you related?.

Related means 'belonging to the same family'. This can be rather broad. I am obviously related to my brother, but I am also related to my great great uncle's son on my mother's side.

We don't typically do mischiefs, we usually make mischief. However, we might do mischievous things.

(At least, that's how I typically hear the word used. Grammatically, though, it's an extremely flexible word – and you've done a “mischievous thing” by asking this vexing question!)

The difference here isn't so much the singular vs. the plural (i.e., mischief vs. mischiefs), it's more a matter of convention: how the word is typically used and what verbs are generally associated with it.

The phrases:

• do mischief
• make mischief
• work mischief
• do mischiefs

all pretty much mean the same thing: the stirring up of impish trouble.

I did some research using Google's ngram tool and found all four phrases of those phrases could be found in published works, and that do mischief was apparently a much more popular phrase in the 19th century.

Collins indicates that the word can refer to:

• irksome behavior,
• an inclination to do the behavior,
• the person doing the behavior, or
• the result of the behavior.

mischief (noun)

1. wayward but not malicious behaviour, usually of children, that causes trouble, irritation, etc
2. a playful inclination to behave in this way or to tease or disturb
3. injury or harm caused by a person or thing
4. a person, esp a child, who is mischievous
5. a source of trouble, difficulty, etc

It's not labeled as a mass noun, but it can function as one. As such, "many mischiefs" would refer to many different acts of mischief, while "much mischief" treats mischief as an uncountable noun.

I can't think of many words that are so adaptable. It would be as if the word food not only referred to what we ate, but also to the process of cooking it, and to the people preparing it as well – as if the word food could function as a synonym for chef and oven. The definitions found at Wordnik are equally versatile.

Having done all that research, I can't find anything grammatically wrong with

He did many mischiefs.

However, it doesn't pass my “ear test.” I can't say that it's never used, but I'll warn that it's probably rarely used in contemporary contexts.

Alexander Pope wrote in a letter:

Such in particular as have the meanness to do mischiefs in the dark, have seldom the courage to justify them in the face of day.

and who am I to tell Alexander Pope that he's wrong? However, I can warn my English learner friends: that language sounds more Shakespearian than contemporary.

I suppose I could tell you that, because the dictionary says it's okay, it must be perfectly normal. But I don't like to be such a mischief so mischievous.