I
conjunction
1
BAD : He hadn't taken any warm clothes with him so that he felt cold.
GOOD : He hadn't taken any warm clothes with him so he felt cold.
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So that is used to express the purpose of an action: 'We took our umbrellas so that we wouldn't get wet.'
So is used to express the result of an action: 'I'd forgotten to take my umbrella so I got wet.'
BAD : Most of these drugs come from the so-called Golden Triangle.
BAD : During the so-called denitrification process, bacteria convert fixed nitrogen into molecular nitrogen.
GOOD : During what is known as the denitrification process, bacteria convert fixed nitrogen into molecular nitrogen.
Use so-called when you want to suggest that the name that has been given to something is incorrect or not suitable: 'I went to see the playwright's so-called masterpiece and was very disappointed by it.'
To introduce the name by which something is generally known, use be known as, be referred to as or be called : 'The distance that light travels in a year is called a light year.' 'Zaire was formerly known as the Congo.'
2
BAD : Since it's his birthday on Monday, so he's having a party.
GOOD : Since it's his birthday on Monday, he's having a party.
GOOD : It's his birthday on Monday, so he's having a party.
BAD : If you're a naughty boy, so the big crocodile will come and eat you.
GOOD : If you're a naughty boy, the big crocodile will come and eat you.
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See also BUT (↑ but )
3
See THAT 3 (↑ that )
II
adverb
1
BAD : During the summer all the hotels are so busy.
GOOD : During the summer all the hotels are very busy.
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Use so + adjective (1) to mean 'to such a high degree or great extent':
'I was so tired that I fell asleep on the train.' 'I didn't expect the hotels to be so busy.'
(2) to express strong personal emotion: 'It was very kind of you to help me. I'm so grateful.'
Otherwise, use very/extremely + adjective: 'She was very tired and found it difficult to stay awake.'
2
BAD : My English is so poor so my wife has to translate everything.
GOOD : My English is so poor that my wife has to translate everything.
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so + adjective/adverb + that clause: 'She was so clever that all the universities wanted her.' 'The pianist played so badly that the audience walked out.'
Compare: 'My English is very poor so my wife has to translate everything.'
3
BAD : We were not prepared for so cold weather.
GOOD : We were not prepared for such cold weather.
BAD : I was annoyed with myself for being so fool.
GOOD : I was annoyed with myself for being such a fool.
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A phrase that ends with a noun ('weather', 'fool') usually begins with such (NOT so ): 'We hadn't expected such a warm welcome.' 'You're lucky to have such delightful children.'
Compare: 'Why is it always so cold in here?' 'The food was so bad that nobody could eat it.'