"Include" vs "involve": usage and difference

Question

I have made some research and found that these two verbs are of similar meaning. Cambridge Dictionary gives this definition of include:

include

verb [T]

to contain something as a part of something else, or to make something part of something else:

• The bill includes tax and service.

• Tax and service are included in the bill.

• [ + -ing verb ] Your responsibilities will include making appointments on my behalf.

And this definition of involve:

involve

verb [ T not continuous ]

If an activity, situation, etc. involves something, that thing is a part of the activity, etc.; and also

If a situation involves someone or something, he, she, or it is affected by it:

• Research involving the use of biological warfare agents will be used for defensive purposes.

• [ + -ing verb ] The operation involves putting a small tube into your heart.

• The second accident involved two cars and a lorry.

What's more, one of the definitions of involve in CALD is:

to include someone in something, or to make them take part in or feel part of it:

So... involve = include?

The first solution I thought of is to define include as "inanimate-inanimate/inanimate-animate" sort of situarion (let us from now on abbreviate inanimate-inanimate as I-I and so on: I-A and A-A). and to define involve as I-A only:

Package (I) includes rice (I) / I-I

Daphne was included on the guest list / A-I

Solomon was involved in the crime / A-I

However... this system just falls apart, and not only because there is an A-I intersection, but because of this

Also because of this (COCA: research involves vs research includes = 102 vs 73)

And because of the same result which BNC gives (frequency of research involves vs includes = 34 vs 14)

My question is: what is the difference, if there is any? Can we say that include is used when we are talking about non-continuous events (shopping list, research as a paper document, etc... in fact, these are not even "events") and, thus, involve is used when we are talking continuous events, finished or unfinished (research as a series of actions, some historical process, crimes, etc)?

This took a little while, so thanks in advance for reading and taking your time to write an answer!

P.S. I've read this thread, but I am nevertheless concerned about the problem as the thread users offered some controversial answers.

Answer 1

The first thing to say is that English has very, very, few true synonyms - if the word is different, there is a difference, at least, in the nuance.

When looking for the differences, there is not much point noting the similarities.

To involve has the literal meaning of "to be wrapped up in" or to be bound in".

To involve something indicates that the object or action takes an inseparable/integral part.

"The experiment involves the use of acid." -> "the use of acid" is an inseparable/integral part of the action of the experiment.

To include merely means that the object is contained within the greater group or whole. The literal meaning of "include" means "to be enclosed within something."

The package with the equipment for the experiment included a letter for Professor Brown.

You will see that something that is involved is also included, but something that is included need not be involved.