Difference between Do and Does

What is the difference between ‘Do’ and ‘Does’?  It can be confusing to decide which form of the word to use in English.  Many people, even native speakers, often mix up these words and use them incorrectly.  The words are related to each other, and in fact, ‘does’ is really a form of the verb infinitive ‘to do’.

The key to using ‘do’ and ‘does’ correctly is to understanding whether the noun in the subject of a sentence is singular or plural.  The subject is the part of a sentence that is about what is being said.  In the example, The big dog does sleep, ‘The big dog’ is the subject or what the sentence is about.  In this case, ‘The big dog’ is singular because ‘dog’ is a singular noun.   It is also necessary to decide what person the subject is in when there is a pronoun being used.  First person singular is ‘I’ and plural is ‘We’.  Second person singular and plural is ‘you’.  Finally, third person singular is ‘he’, ‘she’ or it, and plural is they.

‘To do’ means to make something happen, to perform something, to bring something about or to act or work in a certain way. ‘Do’ is used with all plural nouns, in the first person singular, second person singular and plural and third person plural.  For example:  People do work on a jobsite.  It is used with the pronouns ‘I’, ‘You’, ‘We’ and ‘They’.  For example:  I do things with my friends, and you do things with your friends.  To make the statement negative, ‘not’ would be added after ‘do’.  I do not do things with my friends.

Since ‘does’ is a form of the word ‘Do’, it is used to mean the same exact thing.  However, it is used with singular nouns in the present tense (third person singular).  For example:  The man does work here.   It is only used with the pronouns ‘He’, ‘She’ and ‘It’.  She does what she wants.  It is made negative in the same way as ‘do’, adding not after ‘does’.  It does not belong to him.

‘Do’ and ‘Does’ are also used to make a simple present tense statement a question.  By putting these words in front of a statement a question is now formed.  For example:  You work. Do you work?  When ‘Does’ with the third person (He, She or It), however, the ‘s’ at the end of the verb infinitive is removed.  For example:  He works.  Does he work?  Question words, such as ‘Who’, ‘What’, ‘Where’, ‘When’ or ‘How’ can also be added for additional information.  For example:  Where does he work?  In this case too, whether to use ‘does’ or ‘do’ depends on whether the noun subject is plural or not.

Learning the proper usage of ‘do’ and ‘does’ is quite simple, but only once you understand the underlying grammar.  So when in doubt of which word to use, simply go back to the basics and check to see whether the noun is singular or plural, and if a pronoun is being used, what person it is in.