What are different "what is the dog can do?" and" what can the dog do?"

The right answer is:

"What can the dog do?"

The question is how to make Interrogative sentences?
The sentence is

It can jump (the dog).


To convert a sentence into a question:

  • If it contains an auxiliary verb, we invert the subject and the auxiliary, so "I am singing" becomes "Am I singing?".
  • If it doesn't contain an auxiliary verb, then we add the dummy verb "do" and then invert: "He likes carrots" --> (add dummy auxiliary) "He does like carrots" --> (invert) "Does he like carrots?"

Modal verbs are auxiliaries, so we simply invert the subject and the modal. "He can go" inverts to "Can he go?".

"What is the dog can do" is ungrammatical, because modal verbs like "can" have no nonfinite forms - no infinitives and no participles.

"Can" therefore can't appear as a bare infinitive. It must be replaced with "be able to".

We could ask "What is the dog able to do?". This means exactly the same as "What can the dog do?". Most of the time, we're more likely to use the latter question - it's simpler.

Similarly, we can ask "Can the dog jump?" or we can ask "Is the dog able to jump?".

"To be able to" fills in for those inflections of "can" that don't exist. This is called "suppletion". So we can't say "I will can" (we say "I will be able to") nor "I must can" (we say "I must be able to"). For "must", "to have to" fills in. So we can't say "I might must", but we can say "I might have to".


The non-interrogative is "The dog can do (something)."

To form an interrogative with "can" you invert the subject and auxiliary verb: "Can the dog do (something)?".

You don't form the interrogative of a "can" sentence with "is". *"Is the dog can do (something)" is not correct and would never be formed by a native speaker.

If you are asking a "what" question, then the question pronoun is moved to the front to give "What can the dog do?"

Interrogatives use "is" only when the auxiliary verb is "is". So the statement "The dog is eating (something)" becomes "Is the dog eating (something)" and "What is the dog eating".

  • I agree that the sentence "Is the dog can sit?" would never be formed by a native speaker. However, I might say, "Is the dog home?" or, "Is the dog sick?", or, "Is the dog lonely?". So the problem isn't with is, it's with is ... can. – J.R. Oct 26 '17 at 18:09
  • Yes that is what I thought. But somewhere between my brain and my fingers the thought was lost... I shall edit. – James K Oct 26 '17 at 18:54

The opposite of interrogative sentences is declarative sentences. "To interrogate" basically means "to ask questions". Who are you? What were you doing last Thursday? What is the dog's name? "To declare" means to state something as fact. You are jannie. You were at school last Thursday. The dog's name is Zoe. So if you are going to make an interrogative sentence related to the sentence "It can jump." you have to think of a question what would come before that comment. If you've heard of the game show Jeopardy, think of this like one of the questions from there.

  • Considering that most of our learning audience lives outside North America, I'm not sure how understandable your closing exhortation might be. – J.R. Oct 26 '17 at 18:06

In addition to the standard interrogative reversal of the declarative sentence, you can also ask

What is it the dog can do?

which is semantically equivalent to

What is it that the dog can do?

That is a question that assumes the dog can do something in particular or unusual, perhaps something that most dogs might not be able to do. This dog can dance on its hind legs. But it can also be about the animal "Dog" in general.

What is it a dog can do?

is a question about dogs in general that can be asked by someone who might already know the answer to the question but is trying to elicit a response from another person, as a kind of test, let's say a kindergarten teacher asking a class of youngsters.

A dog can guard sheep.

A dog can be a watchdog.

A dog can be part of a team of dogs that drags a sled.

A dog can lead a person without sight.

A dog can track fugitives from the law using its nose.

A dog can find people trapped in a collapsed building.

A dog can detect illness using its nose.

A dog can detect drugs or explosives using its nose.

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