Sit on the chair vs sit in the chair. Which is very correct?

Some days ago, I saw this question parading itself on Facebook, looking for whom to do justice to it. Well, here is my verdict.

"Sit on the chair" and "sit in the chair". Which is correct? Both are very correct, but these factors should be considered before using either of them: 

• The type of chair
• The intent of the speaker

1. The type of chair
There are different types of chairs (armchair, beanbag, divan, bench, stool, dinning chair etc.), and the type of chair determines your choice of expression, that is, whether you will use "sit on" or "sit in". You use "sit on" for a dinning chair, stool, bench or a chair that has neither arms nor back for you to rest on whereas you use "sit in" for armchairs or any cozy/comfortable chair.

2. The intent of the speaker

In this case, the choice of expression is not determined by the chair type but by the intent of the speaker, that is, what the speaker has in mind. One obvious difference in these expressions ("sit on the chair" and "sit in the chair") is in the use of the prepositions (on and in), and these prepositions are not just there for mere fanciful reasons. When you tell someone to sit in the chair, you are invariably asking the person to make himself comfortable in the chair, which is different from when you use "sit on". That is why you sit in an armchair but sit on a bench, stool or dinning chair.

However, a person might tell his visitor who is very tired and exhausted to sit in a bench or stool for the visitor to have some rest and make himself comfortable. Perhaps that's the only available seat at that time. Judging by the type of chair, it is wrong, but very correct when judged by the speaker's intent, that is, if the intention of the speaker is for his visitor to regain strength by making himself comfortable regardless of the chair type.