In the list or on the list?

​A while ago, a HK client of mine told me "I am putting together a list of people who are willing to volunteer for charity work. Should I ask my colleagues if I can include them in the list, or if I can include them on the list?"

In fact, both the expressions -- include in the list and include on the list -- can be used in English. They pretty much mean the same thing, but they have slightly different implications because of the different prepositions they use. e to edit.

We use the preposition 'in' to convey the sense of being inside a container of some sort. This is often at a very literal level:

• She was trapped in the lift.
• They signed the agreement in the conference room. 

But it can also be used in a less literal way:

• All the information you need is in this document. 

A 'document' doesn't look much like a container, but in this sentence we are imagining the document as something that contains information (like a box or bottle), and that's why we use the preposition in to refer to it. You will often find the preposition in used to talk about things that don't look like containers, but which we nevertheless think of in some way as containing things inside them:

• In my opinion, the opening date should be delayed.   ['my opinion' is here thought of as a container of my thoughts]
• We are planning to expand in the future. ['the future' is here thought of as a container of things that will happen]

By contrast, we generally use the preposition 'on' to refer to the position of something against a flat surface:

• Please hang this picture on the wall.
• Place your hand on my shoulder. 

Like 'in', 'on' can also be used with things that don't look like surfaces, but which we imagine as being like a surface:
​

• I have a lot on my mind today. ['my mind' is here thought of like a flat surface with things piled on top of it. 
  

This brings us back to our initial question: do we include someone in the list, or include someone on the list? The answer is -- it depends on how we think about the list. Is it a container, or a flat surface?

If we think of the list as a container for information, we will probably say 'include in'. But if we think of the list as a surface (say, a piece of paper where we are writing down the names) then we will probably say 'include on'. 

The most common usage in English is 'include in'. We can speaking of including someone (or something) in a scheme, a plan, a proposal, or any other as-yet unrealised activity or intention. That's because we imagine all of these things (schemes, plans, proposals etc) as containers, that can be filled up with details.