Again about articles (
I am reading Harry Potter and the Philosopher's Stone by J. K. Rowling and in the chapter two (THE VANISHING GLASS) I see such paragraph:
...
Dudley’s birthday—how could he have forgotten? Harry got slowly out of bed and started looking for socks. He found a pair under his bed and, after pulling a spider off one of them, put them on. Harry was used to spiders, because the cupboard under the stairs was full of them, and that was where he slept.
...
I don't understand why the author did not use articles before BED (... out of bed ...) and SOCKS (... looking for socks...).
I explain for myself the absence "THE" before "Socks" such way - SOCKS are plural here and it's not important what kind of SOCKS the author meant. If Harry was looking for ONE sock we would see "a sock", wouldn't we?

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Hi Ivan, I'll start with the second question about socks.

Yes, you're right that Harry is looking for ANY socks, even if they don't match. Socks in general. We can't use "the" because that would mean a special pair of socks, and we should already know which one.  We don't need "his socks" because Harry's only searching through his own clothes.

Certain phrases work as adverbs, and these normally don't need articles. Phrases such as "to bed", "in bed" and "out of bed" don't use an article. There are extra nuances: "to bed" means the intention of sleeping; "in bed" means sleeping, resting or feeling unwell; "got out of bed" suggests that you might have things to do. These are not neutral movements.

Can I ask you to explain the rule for using "the", as you learnt it? I suspect there's a misunderstanding there, and it probably isn't your fault.

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Carla and John, thank you very much!!

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Hi Ivan,

YOUR QUESTION: why the author did not use articles before BED (... out of bed ...) 
** "Harry GOT slowly OUT OF BED  [also as;  Harry Got out of his bed] [Harry got out of the bed]

the author/editor may have felt there's no need for a determiner, as it would be redundant because Harry being the 'subject' has been mentioned already

*with  SOCKS
You are right! Harry was just looking for any socks  (to put on and need them right away because it is very cold)

[ using "the +socks" means there's an emphasis to a specificity 
ex: "THE MAGICAL SOCKS", ....a stranger was caught looking for "the socks" under his master's bedroom
[OR in another subject matter]
ex: my daughter's favourite teacher is THE tall guy. After a few months, she was looking for 'the teacher' as she wanted to thank him for his kindness.

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Everybody must take into account when reading the answers that J.K Rowling writes in a style that does not fit any grammar rules you may have learnt. Although this text being discussed is OK. You must remember that J.K ROWLING writes in a style that does not match many grammatical styles that learners may have encountered. "get out of bed" in this passage is a common expression. Normally it would be "get out of THE bed"

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AmericanEnglishMike, thank you very much!