How to use these structures “take something apart” and “put something together”, the “something” is plural or singular?

Question

take somebody/something apart phrasal verb

1 to separate something into all its different parts OPP put together

Tom was always taking things apart in the garage.

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put something ↔ together phrasal verb

3 to make a machine, model etc by joining all the different parts SYN assemble

I can’t work out how to put this table together.

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The example in the dictionary says "put this table together." but why don't we say "put the table's parts together"?

Look at the picture, a pen is made of many different separate parts

So, do you say "don't take it apart" (suppose the speaker and the listener know "it" refers to the pen) or

"don't take them apart" (suppose the speaker and the listener know "them" refers to the separate parts of the pen)?

And, do you say "please put it together" (suppose "it" refers to the pen) or

"please put them together" (suppose "them" refers to the separate parts of the pen)?

Answer 1

For "take (something) apart", people almost always talk about the complete object, because that is the current or starting condition, and it's also just easier to say (usually fewer words, etc).

But "put (something) together" is a little different. In this case, you actually can talk about either the completed object or its parts, but the two do not mean the same thing:

put the table together

This means to put the parts of the table together to form a completed table. The desired end state is important here. If you don't end up with a table when you're done, then you haven't done it right.

put the table's parts together

This means that you're taking parts that could make up a table and putting them together in some way. This might mean that you're just putting them next to each other (side-by-side, or in a pile, etc), or it might mean that you're assembling them, but the way you're assembling them in some way other than the usual way (to make a piece of art, for example). It could also mean that you're assembling them to make a table, too, but it doesn't necessarily say that by itself.

So the reason people use the singular completed object in phrases like "put the table together" is because it communicates information about the thing you will end up with when you're done, which just referring to the parts doesn't tell you.