Here are a few sentences in Mandarin. Which ones do you think are grammatical, and which do you think are ungrammatical?

• 小狗把吃了！
• 小狗把漢堡包吃了！
• 他胖了兩斤。
• 他胖了兩個孩子。
• 個三人在吵架。
• 三個人在吵架。

What information did you use to decide which sentences were grammatical or ungrammatical? I.e., how did you make your decision?

Some people assume that judging a sentence's grammaticality is the same as judging whether a sentence makes sense. In other words, 小狗把漢堡包吃了！ is grammatical because it makes sense, and 小狗把吃了！ is ungrammatical because it doesn't make sense.

Unfortunately, this idea is wrong. It doesn't work.

There are sentences that don't make any sense, but which people still recognize are grammatical. The most famous example is the following sentence from Chomsky:

Colorless green ideas sleep furiously.

People who hear this sentence recognize that it sounds like perfect English; it doesn't break any grammar rules. However, it's hard to explain what it actually means. In fact, it doesn't make any sense. If something is colorless, how can it be green? How can ideas have color? How can ideas sleep?

Another famous example is the poem "Jabberwocky" by Lewis Carroll. Read the beginning of the poem. You will notice that it's nonsense, full of made-up words, but it still has perfect English grammar. You can say who did what to whom, even though you don't know what the words mean. For example: What were the toves like? They were slithy! What did the toves do? They gyred and gimbled! Where did they do that? They did it in the wabe! You can figure out all those things based on the grammar, even though you don't know what the content words mean (because the content words are made-up). It's also quite easy to make Jabberwocky-style sentences in Chinese: for example, 那個很夕淘的涼鋪昨天罷條了一個客批。 Even if you don't know what a 涼鋪 is (because it's a fake word I just made up), you can use the syntax of the sentence to recognize that this 涼鋪 is very 夕淘, and yesterday it 罷條ed a 客批.

All this shows that "grammaticality" is not based on "making sense". There must be some other information you use to decide if a sentence is grammatical.

We are working our way towards another important point about grammaticality. Before we get there, I want you to look at a few more sentences. Below I have written three pairs of sentences. In each pair, what would you say is the major difference between the two sentences?

1. a. I ain't going to the store.
   b. I ain't going store the to.
2. a. 那件衣服很法國。
   b. 那件衣服很在。
3. a. 吃饭了你
   b. 了你饭吃

In each of the pairs in the previous sentence, the first sentence was one that violated prescriptive grammar: it used some words or structures (like ain't, or 很法國 ["very France"]) that people say are not "proper". However, it still follows the descriptive rules of the language. On the other hand, in each of the pairs, the second sentence violated the descriptive grammar. Thus, you should have been able to recognize that in each sentence pair, the first sentence is informal but grammatical, whereas the second sentence is truly ungrammatical.

In fact, when people judge how a sentence sounds, what they are usually judging is acceptability rather than grammaticality. Some people use these terms interchangeably, but to a linguist they mean very different things:

1. Acceptability is whether or not speakers of the language accept a sentence, i.e., whether or not they think it sounds good, sounds natural, sounds 通順, etc. Acceptability is not all-or-nothing, it's gradient: people can recognize that one sentence sounds pretty good, one sentence sounds so-so/麻麻地, one sentence sounds a little bit worse, another sentence sounds quite bad, etc.
2. Grammaticality is whether or not a sentence could have been created using the syntax rules of this language. Recall (from the "Introduction" module) that a grammar is a set of rules/procedures for making language. If you follow these rules and procedures to put sounds together, put words together, etc., you will get a grammatical sentence (even if it's a grammatical sentence that doesn't make sense, like "Colorless green ideas sleep furiously"). Any sentence you say that could not have been created by following those rules is an ungrammatical sentence. Therefore, grammaticality, unlike acceptability, is all-or-nothing: a sentence is either grammatical (follows all the descriptive grammar rules of the language) or it is not.

Sentence acceptability is influenced by many things, and grammaticality is only one of those things. Usually, if a sentence is ungrammatical, it will also be unacceptable, because it sounds bad to people. But this is not always the case.

We can create sentences that are grammatical but not acceptable. For example, I heard that John said that Divya hoped that Sally demanded that Karl insisted that the cat wanted to go to the park that Andrew told me to take the car with the broken wheel that Suzy tried to fix yesterday to. That sentence does not violate any rules of grammar, but many people may consider it an unacceptable sentence. (If it sounds ok to you, keep in mind that I could keep adding more stuff and make it 10 times longer.) Other examples are center-embedded sentences:

• Dogs cats rats bite chase escape.
• 闻到吓到小狗的小猫的老鼠逃跑了。

The two center-embedded sentences above are both grammatical, in that they do not violate any rules of grammar; in fact, they are meaningful sentences. For example, dogs cats rats bite chase escape means: there are some cats that rats bite; there are some dogs that chase those cats, and those dogs escape. (If you're interested, you can try to figure out why. A hint: "dogs cats rats bite chase escape" has the same sentence structure as "Cars the company I run sells are efficient." We will revisit these kinds of sentences in the Psycholinguistic Processing module.) Nevertheless, they are very hard to understand, and most people will say they aren't acceptable sentences.

Things work the other way as well. There are sentences which are ungrammatical (i.e., they violate a rule of grammar), but which native speakers find acceptable, and sometimes don't even notice the grammar error. Here are three examples of sentences which were produced by native English speakers and which each have an un-noticed grammatical error. Can you figure out what the grammar error is? (All three sentences have the same type of error.)

1. Columbia Road Baptist Church has fully cooperated with the authorities and have nothing to add. (source [content warning: sexual violence])
2. The fight over DeVos has gotten multiple Republican senators — including very conservative ones like Jerry Moran of Kansas — to restate his opposition to the idea of a federal school voucher program. (source)
3. The suspected actions of one crazed individual doesn't justify the vilification of millions of peaceful Trump supporters. (source)

The main point of the previous exercise was to see that acceptability and grammaticality are not the same thing: grammatical sentences can be unacceptable, and ungrammatical sentences can be acceptable. For a more technical discussion of this point, you may read Norbert Hornstein's blog post "Judgments and grammars" if you are interested.

The goal of syntax is to figure out what the descriptive rules of a grammar are (specifically, the rules about how to make phrases and sentences in a given language). This is done by figuring out what's grammatical and what's not. But you may have noticed that this is circular: "grammaticality" depends on the rules of the language, so we can't know what's "grammatical" if we don't know what the rules are, and we can't figure out what the rules are if we don't know what's grammatical.

In practice, syntacticians usually use acceptability judgments as a proxy for grammaticality: if a lot of native speakers agree that a sentence is bad, syntacticians will conclude that it's probably ungrammatical, and use that information to try to figure out what the grammatical rules of the language are. But keep in mind that syntacticians always have to be careful to avoid other factors that might influence acceptability judgments. They want to make sure that, if native speakers say "this sentence sounds bad", they are saying that because of the grammar issue and not because of other things (such as the sentence being long, or hard to understand, or stuff like that). In this sense, syntax is like any other science: it's important for one's experiments to be carefully controlled to avoid confounding factors.

Can you think of any more examples of sentences that are grammatical but unacceptable, or sentences that are ungrammatical but acceptable? (In any language.)