It is happy to eat delicious cake

[i0pepper]

Hello, my students keep writing "It is happy to read interesting books," "It is happy to see my grandfather," etc. My co-worker from England says "happy" should be "fun" or "enjoyable," but we don't know why.

Could someone help us? How can we explain this to our students?

[Teia]

Hello, my students keep writing "It is happy to read interesting books," "It is happy to see my grandfather," etc. My co-worker from England says "happy" should be "fun" or "enjoyable," but we don't know why.
Could someone help us? How can we explain this to our students?

Hi

Your co-worker is right. You cannot use the impersonal pronoun in this construction. "It" is used as an impersonal subject of the verb "be", especially to refer to time, distance, weather or in identity constructions.
e.g. It was a nice day yesterday.
It is 3 o`clock p.m.
It is a long distance to the nearest town.
This is my dog ;it[my dog] is happy now though it has been sick this morning.

For further details regarding the use of impersonal "it" see :
http://dictionary.reference.com/search?q=it

to be happy to see a person:

I am happy to see my grandfather, or
You / we/they are happy....
He/She/It is happy to see....

but [as your co-worker told you ] you can say :
It is fun/enjoyable to see somebody, etc.

She is full of fun./ I am full of fun etc. or,

A picnic would be fun.

Hope you understand the use of "it"

Best wishes,

[Dany]

Happy is more used to describe that you are glad about something. e.g. "I am happy to see you".

If you want to describe what you like, then "fun" or "enjoy" is much better.

[riverkid]

Hello, my students keep writing "It is happy to read interesting books," "It is happy to see my grandfather," etc. My co-worker from England says "happy" should be "fun" or "enjoyable," but we don't know why.
Could someone help us? How can we explain this to our students?

Your students are mixing up a collocation that is natural to their language so they think it is/should be natural for English. This comes from the terrible manner in which they are taught English, the grammar translation method. You'll run into a lot more of these.

There are many ways to construct possible grammatical sentences but not all will be English.