I
conjunction
1
BAD : It is two months now that I left Germany.
GOOD : It is two months now since I left Germany.
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a week/two months etc + since something happened (NOT that ): 'It's almost two years since I started my PhD.'
2
BAD : I was shocked by the sight that I could hardly speak.
GOOD : I was so shocked by the sight that I could hardly speak.
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so + adjective/adverb + that clause: 'I'm so tired that I can't keep awake.' 'He spoke so quickly that nobody could understand him.'
3
BAD : He closed the door quietly that nobody would hear him.
GOOD : He closed the door quietly so that nobody would hear him.
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Use so that to express purpose (NOT that ): 'The burglars turned off all the lights so that they wouldn't be seen.'
4
BAD : Children are not as easy to please nowadays that they were in the past.
GOOD : Children are not as easy to please nowadays as they were in the past.
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When making a comparison, use as/so ... as (NOT as/so ... that ): 'It's as hard to get into university today as it was ten years ago.'
5
BAD : It worried me that the letter had not arrived, especially that it had never happened before.
GOOD : It worried me that the letter had not arrived, especially since/as it had never happened before.
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When giving a reason for something, use since or as (NOT that ): 'Instead of cooking, why don't we get a take-away, especially as it's so late.'
II
pronoun
1
BAD : The weather has been very good, except for two days that it rained.
GOOD : The weather has been very good, except for two days when it rained.
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When the meaning is 'at/on/in/during which' (referring to time), use when (NOT that ): 'These are the times when Dr Roberts will be able to see you.'
Compare: 'I shall always remember the two days that I spent in Paris.'
2
BAD : Sitting next to me was an old lady, that seemed to be sound asleep.
GOOD : Sitting next to me was an old lady, who seemed to be sound asleep.
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That is used to introduce an identifying relative clause (one which identifies, defines, or restricts the preceding noun): 'The woman that is sitting behind us is Tom's music teacher.' 'The man that I marry will have lots of money.'
That is not used to introduce a non-identifying relative clause (one which simply adds more information about the noun).
3
BAD : If you haven't sent it yet, I'd be pleased if you would do that as soon as possible.
GOOD : If you haven't sent it yet, I'd be pleased if you would do so as soon as possible.
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To make a precise reference to a previously mentioned action, use do so (NOT do that ): 'I asked him politely to take his feet off the seat but he refused to do so.'