We are dancing in the sea

It is a common law of the universe that events can only happen in the present moment.  But in speech, we are able to describe them in the past, the present or the future, which is why languages have developed tenses to sort this out!  For the moment (now!) let us have a look at how the present tense can be used.

With English there are two main ways to describe things in the present tense.  For example with this picture of two people dancing in the sea.

They are dancing in the sea.    (present continuous)
They dance in the sea.       (simple present)

Non-native speakers will often use the simple present tense to describe a present action, when often it is the present continuous tense that is needed.  So with our example – what are the couple doing?  The answer:  ‘They are dancing in the sea’ means that they are dancing now.  The action (dance) is still in progress so we use the verb ‘to be’ with the -ing form of the action verb.  

With the simple present the question would be e.g.  ‘What do the couple do at the weekend?   Answer ‘They dance in the sea”.  This is because the answer doesn’t refer to the present moment, and the action of dancing is not currently in progress. Describing any ‘now’ action without using the verb to be +ing is not really correct English.  For example,  ‘I read a book’, or ‘I go to the shop’, both require a point in time to give better meaning (i.e.’I go to the shop after work’, and ‘I read a book at bedtime’).