When to use Does and Is while starting the Interrogative sentence?

Question

I am confused which is the correct sentence

• Does your company works on php?
• Is your company works on php?
• Do your company works on php?

Answer 1

Questions are formed by inverting the word order from the usual Subject-Verb ("I am", "I do") to Verb-Subject ("am I", "do I").

Auxiliaries - If the verb is a form of an auxiliary verb such as "be", "have", "shall", "will", "may", "must", you simply perform the inversion on the original sentence. (An auxiliary is a helping verb that combines with another verb to express tense, aspect or mood.)

So:

• "I am going there" becomes "Am I going there?".
• "She will be there" becomes "Will she be there?".
• "I have seen it" becomes "Have I seen it?"

If the verb is "be" then you still perform the inversion in this way even if "be" isn't acting as an auxiliary. So:

• "She is sad" becomes "Is she sad?"
• "He is there" becomes "Is he there?"

If the verb is "have" acting as a main verb (not as an auxiliary) then this is possible too (though not mandatory). So, optionally:

• "She has a car" can become "Has she a car?"

The dummy auxiliary 'do' - For all other verbs (and optionally for "have" as a main verb), the dummy verb "do" is introduced. In an ordinary declarative (S-V) sentence, "do" is a marker of emphasis, whereas in a Verb-Subject sentence, "do" is purely a question-marker. ("I do see it", "she does know", "he does drive".)

It is important to note that "do" is an auxiliary.

Non-finiteness of main verb as part of a complex tense etc. - Where there is a complex verb (auxiliary plus main verb), the main verb takes a non-finite form, either a participle (where the auxiliary is "be" or "have") or an infinitive (so the 3rd person singular, or he/she/it, form lacks an '-s' ending). Hence:

• "She must go" (not "goes")
• "He might know" (not "knows").
• "It does work" (not "works").
• "It will fly" (not "flies").

Similarly, once inverted, the main verb must remain non-finite. So:

• "It is working" --> "Is it working?"
• "I have eaten" --> "Have I eaten?"
• "She must go" -->" Must she go?"
• "It will fly" --> "Will it fly?"
• "It works" ("It does work) --> "Does it work?"

Hence, "Does your company work on PHP?" (not "works"). "Does" is an auxiliary. The sentence is formally the inverted form of "your company does work on PHP".

"Is your company working on PHP?" (not "works").

"Do your company work on PHP?" (not "works") - if you regard "company" as a collective noun (being treated as a plural).

"Does" is the 3rd person singular form (he does, she does, it does). "Do" is used for the other persons and in all plural persons.

See also: https://learnenglish.britishcouncil.org/en/english-grammar/clause-phrase-and-sentence/verb-patterns/verbs-questions-and-negatives and https://www.englishgrammarsecrets.com/questions1/menu.php

Answer 2

It depends on what the sentence would look like if you phrased it as a statement rather than a question: in particular, what is the main verb, and whether there is a modal / auxiliary verb (must, will).

For sentences with a modal, you simply move the modal to the front:

You will need a car
Will you need a car?

If there is no modal and the main verb is be, you move the main verb to the front:

This is your hat
Is this your hat?

If there is no modal and the main verb is not be, you add do, and convert the main verb to a bare infinitive:

Your company works on PHP?
Does your company work on PHP?

have is complicated, because it can be either modal or not.

You have seen him. -modal
Have you seen him?

You have got a car - modal
Have you got a car?

You have a car - non-modal
Do you have a car?