when to use preposition 'to' or 'for'

Question

I am searching for

or I am searching to

necessary for

or

necessary to

I am confused with the usage of 'to' and 'for'. Can somebody help me to apply the proper preposition?

Answer 1

Here, we are talking about the 'verbing' -searching.

Okay, the good point I can think of is... when you use 'searching for' as a verb, immediately what follows it is 'noun'.

I'm searching for a pen

On the other hand, if you are using 'searching to', it is followed by a verb.

I think all of us have to do some soul searching to figure out how does something like this happen.

Said that, it depends, what are you searching! If they are 'things', you search 'for' them, if it's action, you search 'to' it.

Same thing is with 'necessary'. OALD has an entry for that:

necessary for somebody/thing

And...

necessary to do something

The example follows:

It may be necessary to buy a new one.
It doesn't seem necessary for us to meet.