Existence in English

Rule 2: Existence (There Be)
Perhaps the most comment mistake made by Brazilian students of English is when they express the idea of 'existence'.
This is due to the variety of forms that Portuguese offers to express existence:
Há...; Tem...; Existe...

In English, There (Be) is used to express Há.. (houve, haverá); Tem... (tinha, terá); Existe etc.

The subject 'There' is used to fill the subject position of the sentence.
The linking verb 'Be' is conjugated for tense and modality to introduce the predicate.
Subject + (Be) + Predicate
Ex. (There) is (a problem). (present tense)
There are several mistakes in the text. (present tense/plural)
There was a bad accident on the highway last night. (past tense)
There were many exercises to do in our English class yesterday. (past tense/plural)
There has been a dramatic increase in sales this quarter. (present perfect)
There will be an audit of this department next month. (future)

Note 1: Contraction of 'there is' and 'there are'; 'There has been' and ' there have been'
In spoken English, it is very common to contract 'There' and 'is' or 'are' and say:
There's. There's is used even if the predicate noun is plural or singular:
Ex. There's a letter on the shelf for you. (singular noun)
There's some spaghetti in the pot for you. (non-count noun)
There's many decisions to make before we can continue. (informal plural)

You can also contract 'there has been' and 'there have been' in a similar way:
Ex. There's been a great improvement in your work recently. (singular)
There's been days when i just wanted to quit. (informal plural)

Note 2: 'There is' not 'Have '
Portuguese speakers often use 'Have' to express the same idea as 'There is'. This is because the verb 'Ter' is often conjugated and used as the verb of existence.
'Ter - tem'; 'Haver - há'; 'Existir - existe' are classified as impersonal verbs and therefore don't have subjects in Portuguese. But, in English, the subject is constant when a verb is conjugated so English gave this function to the subject 'There', making it a constant when we express existence.
Ex.
Tem - There is/are
Tinha - There has/have been
Teve - There was/were
Terá - There will be/There's going to be
Teria - There would be
Deve ter - There should be
Pode ter - There could be/There may be
Tem que ter - There has to be/There must be
Poderia ter tido - There could have been

Note 3: When students make this translational mistake in class, then I often remind them of the following: "Se ninguem tem, então não use 'Have' em inglês." (If nobody has something, then don't use the verb 'Have' in English. This is because 'have' often represents possession and never represents existence. Also, any conjugation of the verb 'have', must have a subject.

Note 4: Question Forms
When we ask about existence, then the first auxiliary/linking verb takes first position in the sentence, inverting with the subject.

Affirmative Interrogative
There is... Is there...?
There was... Was there...?
There has been... Has there been...?
There will be... Will there be...?
There would be... Would there be...?

Note 5: Negative forms
When expressing negative existence then we negate the first auxiliary/linking verb.
affirmative negative
There are... There aren't...
There were... There weren't...
There have been... There haven't been
There will be... There won't be...
There would be... There wouldn't be...