confusabledifferenceprepositions
This question always confused me and finally I decided to know which one is correct and wrong!
Can we use "for" and "to" interchangeably?
for example:
He always goes to the confectionery to buy some cake
And
He always goes to the confectionery for buying some cake
Let's get the easier question out of the way first. When you are confused, you can use about or on, but I think about is the "safer" choice. Behold the ngram.
As for for the taking, let's say that you need a job, and I own a business. I might tell you:
I have a job opening. It's yours for the taking.
or:
I have a job opening. It's there for the taking.
Basically I'm telling you that you could get a job with me, if that option sounds good to you. I could easily substitute "if you want it" for "for the taking".
Looking at the ngram, we see that common ways to use the phrase include
I won't say those are the ONLY way the phrase can be used, but an answer can't delve into every possible usage of a phrase. Those three are a good start.
There's also a relatively high number of
but those come mostly from legal documents; that's not a wording generally heard in everyday conversation.
Of and about are by far the most common, and mean essentially the same thing.
In fact, when we look specifically for "I'm thinking * buying", any other choice is so rare it might as well not exist. The author you quote as writing "I'm thinking on buying..." might be using a regionalism.
Best Answer
Prepositions often have overlapping usages, but that's not quite the same as "interchangeable". In your examples, notice how you had to switch the form of the word buy to make both sentences sound okay.
Both for and to can be used to explain a reason or motivation for something. However, when used in this way, to is followed by a verb, but for is followed by a noun. Consider:
Here's another interesting example:
In this case, the sentences are the identical except for the preposition. However, does this mean the two words are interchangeable? No, it doesn't! These two sentences are both acceptable only because study can function as a noun or as a verb. So, in the first sentence, study functions as a noun, aligning with meanings 8a at Collins:
In the second sentence, the two-word phrase to study functions as an infinitive, and therefore study is used as a verb, meaning:
I agree with some of the comments about your two sentences; that is, I think "to buy some cake" sounds better than "for buying some cake." But I can see why you'd be confused by this, because we can find some very similar sentences in published books, like:
We could change those sentences to read: to walk your dog, to bathe older adults, and to get a license; any differences in meaning would be minimal. However, sometimes such changes will sound natural and acceptable, and sometimes they won't.
Most importantly, remember that little words like for, in, of, at, with, on, and to are extremely flexible. They typically have several meanings and are used in various ways, including phrasal verbs and prepositional phrases. It will be difficult, if not impossible, to pick two of these words, and give you foolproof guidance that will help you know "which one is correct and wrong." When it comes to these little words, there are simply too many variations to explain everything succinctly.