Source: Swan. M. 2005. Practical English Usage Oxford, United Kingdom: Oxford University Press (2011).
Practical English Usage lists over a hundred common mistakes in the English language. Listed below are a number of mistakes that intermediate students of English often make according to Swan (2005).
“I promise I pay you tomorrow.” = I promise I will pay you tomorrow.
(217.3) We often use will in promises and threats. Note that the simple present is not possible in these cases.
“This is the first time I’m here.” = This is the first time I have been here.
(591.1) We use the present perfect in sentences constructed with this/it/that is the first/second/third/only/best/worst etc.
“I’ve been here since three days.” = I have been here for three days.
(208.1-2) For and since can both be used with a present perfect to talk about duration up to the present. They are not the same. Compare: for + period; since + starting point. We use for for duration – to say how long something lasts. To measure the duration up to the present, we use a perfect tense, not a present tense.
“If I’ll have time, I’ll go home.” = If I have time, I’ll go home.
(257.2) In an if-clause, we normally use a present tense to talk about the future. This happens after most conjunctions.
“If I knew the price, I will tell you.” = If knew the price, I would tell you.
(258.2) To talk about unreal or improbable situations now or in the future, we use a past tense in the if-clause (even though the meaning is present or future), and would + infinitive (without to) in the other part of the sentence.
“He said me that he was Chinese.” = He told me that he was Chinese.
(504.1) Both say and tell are used with direct and indirect speech. (Say is more common than tell with direct speech.) Tell is only used to mean ‘instruct’ or ‘inform’. So we do not use tell with greetings, exclamations or questions, for example.
“She told me she has a headache.” = She told me she had a headache.
(275.4) After past reporting verbs, we usually change the original tenses even if the things the original speaker said are true.
“There’s the man that I work for him.” = There’s the man that I work for.
(428.6) We do not use personal pronouns to repeat the meaning of relative pronouns. (494.7) As subjects or objects, who(m), which, and that replace words like she, him or it: one subject or object in a relative clause is enough.
“I’ve told you all what I know.” = I’ve told you all (that) I know.
(497.2) What is only used to mean ‘the thing(s) which’. It cannot be used as an ordinary relative pronoun after a noun or pronoun. (498.4) Instead, that is often used in identifying relative clauses instead of who/whom/which. That is most common as an object, or as a subject instead of which. (584.1/5) We can usually leave out the relative pronoun that when it is the object in a relative clause. Also, we can often leave out the conjunction that, especially in an informal style.
See other: Notes On English Grammar