So do I

Such a commonplace expression. We use it and similar expressions day in, day out.

“I like truffles.”

“So do I.”

“I’m tired.”

“So am I.”

“I don’t like coffee.”

“Neither do I.”

But have you ever thought about what you need to know in order to correctly utter a little response like that?

Probably not. You have better things to do with your time. I can’t remember thinking about it either until the other week, when I had to prepare a language lesson on this very point for students learning English as a foreign language. Allow me, then, to enlighten you about part of what you’re unconsciously doing when you use one of these expressions.

First of all, you’re determining whether what the other person has said is positive (“I like truffles”), or negative (“I don’t like coffee”). If it’s positive, you begin your reply with “so”. If it’s negative, you begin with “neither”.

Secondly, you’re deciding which verb to use. If the other person has used a form of “have” or “be” (e.g. “I’m tired”), you use a form of the same verb in your reply (e.g. “So am I”). If the other person hasn’t used “have” or “be”—ta da! You drop in a form of the verb “do”, instead, like this: “I like truffles” – “So do I!”. Not, you will note, “So like I”.

Thirdly, you’re choosing the correct verb form. If someone refers to a past event and tells you, “I was tired”, you’d reply “So was I”, whereas if they tell you how they’re feeling right now (“I am tired”), you’d respond “So am I”.

Lastly, you’re keeping a firm grip on word order. Although the first person’s statement follows the normal pattern of subject and then verb (I like/I was/I did/etc.), you know you have to switch that order in your reply and say “So am I”, not “So I am”.

And to think that you did all that without even realising. Clever, huh?

It is amazing how children learning their native language pick up so much without having to be explicitly told. They figure out rules and patterns all by themselves. One of the most obvious ways you can see this is when you hear a toddler saying “I goed outside.” The little chap knows that to make the past tense of a verb you add “ed”. What he doesn’t yet know is that that rule, like so many others in the English language, has exceptions—in this case the nefarious little beings known as “irregular verbs”. He’s grasped the rules of the game and he’s doing his best to follow them. You can’t blame him if the verbs don’t play fair. He’ll learn how to deal with them in time.

What linguistic complexities we dance through every day without so much as a thought!

What was that you said? You think it’s fascinating?

So do I.