Mir ist heiß/Ich bin heiß
Okay, firstly, I know the difference between the two phrases - when I was a kid I lived in Germany and I remember my mum telling me of an incident at the class where she and my dad were learning the language in which a very attractive woman was asked to say that she was hot. She said "ich bin heiß", and made the tutor go bright red. So I know the difference. What I want to check is if I've got the reason for the difference right.
"Mir ist" is Dative, whereas "ich bin" is Nominative. So am I right in saying that "mir ist heiß" is Dative because it's heat as an outside force acting on you, whereas "ich bin heiß" is a statement about an inherent quality that you have and therefore must be Nominative?
There are just certain adjectives that are used with dative if you want to express a subjective feeling. "Ich bin heiß" may have a second meaning that made the tutor go red, but first and foremost, it's an objective statement: "I am/my body is hot." You can say it when you have a fever. "Mir ist heiß", on the other hand, is just a statement about how you feel. Everyone else around you might be freezing, your body temperature might be icy, but what you feel is that you feel hot.
This works with several adjectives:
Mir ist kalt/ heiß/ warm.
Mir ist schlecht/übel/schwindelig/elend.
Mir ist unheimlich.
Mir ist langweilig.
And there are some who need a subject:
Es ist mir egal/recht/einerlei/zuwider.
Es ist mir neu.
Es ist mir peinlich.
...and a few others. A few of them show pretty well what I mean, there is a great difference between "I am scary" and "I feel scared".
Some helpful context:
Ich bin unheimlich = I am scary (to you); Mir ist unheimlich = I feel scared
Ich bin langweilig = I am boring (to you); Mir ist langweilig = I feel bored
So, in the same vein:
Ich bin heiß = I am hot (to you); Mir ist heiß = I feel hot
Not really. Ok, in this case the explanation makes sense but you can't transfere this rule onto other sentences. (Like: I got knocked over. - Ich wurde überfahren. - involves an external force but uses the Nominative.)
In primary school they teach special questions to get the right case.
"Wer oder was ...?" indicates Nominative ("Wer oder was ist heiß?" - "ICH bin heiß." = Nominativ).
And the question "Wem oder was ..?" indicates Dative ("Wem oder was ist heiß?" - "MIR ist heiß." = Dativ).
Additional: Genitiv= "Wessen ... ?" ("Wessen Auto ist das?" - "MEIN Auto ist das")
Akkusativ = "Wen oder was ...?" ("Wen oder was liest du?" - "DAS Buch lese ich.")
So it's idiomatic? Wow I didn't know (as the OP (original poster stated you know already) I called my friend after this and she said the same not to repeat like I was with the Ich bin.