ศาลาชุมนุม

[r2d2]

A reply from a beginner, for what it's worth.

I found (find) this difficult as well. The way that I understand it is that คือ means 2 things are equivalent a bit like the "=" symbol in maths. On the other hand เป็น is more general and descriptive. eg, in English. John is my teacher. This is an equivalence relation, it's specific and works the other way round, My teacher is John. So we would use คือ

John is a teacher is more descriptive and we can't say A teacher is John, because Tom, Dick and Harry are also teachers. So it is not "=" and we use เป็น

It is quite likely that I have this totally wrong

To be or not to be (Shakespeare)

คือหรือไม่เป็น(ไร)
To เป็น or not to คือ, that is the question (of Peter).

I got caught by your "John is my teacher. This is an equivalence relation, it's specific and works the other way round, My teacher is John."

I am teacher ผมเป็นครู
Teacher am I ครูเป็นผม

Seems not to work?!

ครู(ของ)คุณ((เป็น???)ชื่ออะไร
ครู(ของ)ผม(เป็น???)ชื่อจอห์น

We learnt here, some monthes ago (a surprise for me), that ชื่อ is a noun but not a verb.
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Edit: I'm actually caught by your "John is my teacher" and "My teacher is John." And I'm also beginner ... no, that is not correct ... started long ago but made little progress in the meanwhile ... in Thai grammar. (ชื่อ)/คือ/เป็น is a field where I feel really unsure.

Reconsidering my original post I feel that I was caught too much by the usage of a name. May I expand it differently:

เด็กกินข้าว
ข้าวกินเด็ก

This turn of position does not work in Thai without changing the meaning completely. The same in English (in languages [still] using declensions you could do this exchange without changing the meaning): "The child eats rice." "The rice eats child."

The difference in-between the sentence with child an "John is teacher." vs. "(The) teacher is John"?

The child-sentence uses a 'full verb' while the John-sentence uses this kind of 'auxiliary' where we Western learners are always stumbling about in Thai, to be, to have etc. ...

เด็กสวย: A nice and complete Thai sentence. It is not incomplete for the fact that is missess an 'auxiliary verb'. No help is required to understand the sentence.

What I want to say: At the level where most Western languages are using 'auxiliary verbs', Thai is more specific.

But ... I wouldn't say that "คือ can nearly always been replace by เป็น but not inversely".

นี่คือรถใหม่ของฉัน = this is my new car.

...can I use เป็น here insted of คือ if i reconstruct the sentence

Peter

Re-reading my first mixing-in: Yes, a simple replacement of คือ by เป็น will change meaning of the sentence under discussion, and yes, if Peter is reconstructing his sentence he may be able to say the same while using คือ or เป็น each. And we Thai learners have to understand how to use these not-auxiliary verbs appropriately, i.e. to find out what we want to say in effect.

[Toffeeman]

Had an interesting example of the misuse of เป็น and คือ yesterday. I was out with some Thai friends and the weather turned bad so I asked my friends: พยากรณ์อากาศคืออะไร? The answer I got was a definition of the word weather forecast.

So explained I know what it is but what is going to happen today? So they said I should say พยากรณ์อากาศเป็นอย่างไร?

Another lesson for me in the use of 'how' in Thai having the same meaning as 'what' in English but also the fact the word คือ in minds of the Thais was obviously a question about defining a word even though in my mind the context of the fact that it had just started raining should have been enough for them to work out my meaning. Anyway another lesson learned of how to say things the way Thais say them and to stop translating from English.