Difference in usage between "to" and "for"

Question

Is there a difference between 2 following phrases:

1. What running can do for your heart.
2. What running can do to your heart.

Answer 1

The word to suggests a direct relationship between the nouns themselves, when two or more nouns are involved. For example:

I did something to you.

We can also say:

She did something to them.

They did something to him.

The above first example suggests that the relationship between these two people is that something was done towards the second noun, by the first noun. This is why, like JMB previously mentioned, to is very neutral: whether the 'something' was a good thing or bad thing, it would have been done to the actual person. Therefore the connotation of to depends on the nature of the act itself - it can be positive or negative.

On the other hand, for suggests a relationship between one noun and and the other noun's state of being. For example:

I did something for you.

Again, we can also say:

She did something for them.

They did something for him.

The first example suggests that the relationship between these two people is that something was done towards the second noun's state of being, by the first noun. Whether the 'something' was a good thing or bad thing, it would have been done for the sake of the person.

And since doing something for someone else's sake generally carries the implication of affection - which is a positive thing, it has a more positive connotation than to.

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If you apply this thinking to the two sentences in the question, then it can be observed that:

What running can do to you heart...

is simply suggesting a connection (you as the reader are left to ponder if the author meant it in a positive way, a negative way or simply didn't mean anything at all), while:

What running can do for your heart...

is suggesting a connection, and also suggesting that the connection is a beneficial one for the second noun (the heart).

Answer 2

Yes.

"For your heart" will talk about positive things that running can bring while "to your heart" is more neutral, and could lead to explaining the good things and bad things.

Hence, for general comments on the effects, use "to", and for positive benefits, use "for".

You might also see "for" used in advertising by companies to entice customers:

Click here to find out what we can do for you!

A news article about an economic crisis might read:

The damage it did to the economy was devastating.

And in a period of boom, the headline might read:

Small businesses good for economic growth

Answer 3

This is how I see the difference.

To expresses a negative action, an aggression (here) to your heart.

Running can be harmful to your heart if you run too fast, too far and too often.

For expresses a positive action, it's like a gift.

Running regularly at a moderate speed can be very good for your heart.

Answer 4

There are some cases where they both differ in meaning,

For example, consider the sentence

I'm doing this 'for' you

Here, I'm doing 'the thing which is to be done by you' for you. I'm substituting you in doing the work.

The same sentence if said

I'm doing this 'to' you

Here, i'm doing the thing to you, It maybe a good/ bad, etc. Eg: I'm doing good to you. So here the result of the work is directed towards you.