For starters we begin with the twelve tenses in Active Voice.
The TENSE in English grammar falls under three main heads and each one has four kinds in it.
And each of the four kinds in each of the three heads has its own formula and function.
Let’s discuss each TENSE in some detail:
One verb or two verbs or three verbs…?
What we should remember is that not all the verb words we see in a sentence are verbs of that sentence because some verb words are not verbs at all — the non-finite verbs; some verbs acting as helping verbs are not taken as main verbs; some sentences have only one verb and some have more than one verb, and some verbs are only one part verbs and some others are more than one part verbs!
This is a big book.
He has read this book.
We have been waiting for him.
In the first sentence ‘is’ is the verb – one Main verb with only one part – simple present tense.
In the second sentence ‘has read’ is the Verb – one verb with two parts – ‘has’ — helping verb; ‘read’ – the past participle V3 form of the main verb ‘read’ – present perfect tense.
In the third sentence ‘have been waiting’ is the verb – one verb with three parts – ‘have’ & ‘been’ – helping verbs; ‘waiting’ — the present participle (ing) form of the Main Verb ‘wait’ – present perfect continuous tense.
Now look at these sentences…
He was crossing the road when I saw him.
We shall have been doing this course for five months by the time you return from training.
In the first sentence there are two verbs: ‘was crossing’ and ‘saw’ — ‘was crossing’ – one verb with two parts – ‘was’ – helping verb; ‘crossing’ – the present participle (ing) form of the main verb ‘cross’ — past continuous tense; ‘saw’ – one verb with only one part – simple past tense. In the second sentence also there are two verbs: ‘shall have been doing’ and ‘return’ — ‘shall have been doing’ – one verb with four parts – ‘shall’, ‘have’ & ‘been’ – helping verbs; ‘doing’ – the present participle (ing) form of the main verb ‘do’ – future perfect continuous tense; ‘return’ – one verb with only one part – simple present tense.
A SIMPLE SENTENCE takes only one Verb with any number of parts in it but COMPOUND, COMPLEX AND COMPOUND-COMPLEX SENTENCES take more than one Verb with any number of parts (maximum four parts) in each verb, depending on the context.
There are a couple of important points related to TENSE we all must learn.
when the subordinate clause comes after “than”, the main verb in this subordinate clause may be put in any TENSE required by the context:
a) He demanded a higher price than she could pay.
(‘demanded’ – simple past; ‘than’ – conjunction; ‘could pay’ – simple past)
b) He demanded a higher price than she can pay.
(‘demanded’ – simple past; ‘than’ – conjunction; ‘can pay’ – simple present)
when the verb in the introductory clause is in the PRESENT OR FUTURE TENSE,
the verb in the subordinate clause may be in any tense that the context requires:
a) He thinks that she is there. [simple present — simple present]
He thinks that she was there. [simple present — simple past]
He thinks that she will be there. [simple present — simple future]
b) He will think that she is there. [simple future — simple present]
He will think that she was there. [simple future — simple past]
He will think that she will be there. [simple future — simple future]
And there are some more important points related to Direct-Indirect Speech, so please go to the topic of DIRECT-INDIRECT SPEECH!