I turned to my friend.
The fought to the last man.
The road was parallel to the river.
I would like to go to London.
What is the key to success?
I have decided to eat.
I am waiting to go home.
‘ What is the key to success?’
In such a way,’key ‘ does not mean only ‘ a piece of metal ‘.
It’s the thing that you must do in order to achieve something.
‘ This is the key to validatING.'( not validate = not infinitive )
In this case,’ the key ‘ means the best or only way to achieve something.
However,why is the preposition of ‘ To ‘ not followed by ‘ infinitive in the previous
Non- native people who are in also other
countries think that ‘To ‘ is followed by ‘ infintive’.
But,we often see that ‘To’ is followed by ‘ ING- form ‘.
It seems almost people do not achieve the answer To the enruiry .
Ultimately,I think that the key is a word of ‘ key ‘.
Because,there is a rule that ‘ key ‘ is followed by ‘ to ‘.
There is also rule that ‘ answer ‘ is followed by ‘ to ‘.
It is the same rule as ‘ road ‘ is followed by ‘ to ‘.
So,the sentence does not include ‘ to-infinitive ‘,using verb ,though.
Perhaps,native people want to express the word after ‘ to ‘ as like noun for direction or destination.
For example,it means that ‘ the road to West ‘.
Look at the sentence,’ This is the key to validating.’ again.
‘ Validating ‘ is used as ‘ Noun ‘ using ‘ Ing-form ‘ after ‘ To ‘.