Thanks for the suggestion. That is how I would write it (see the bottom of my original post), but this was just some example sentence to illustrate the quesetion.
Dependence is the state of having a dependency on something. Dependency is the state of having to depend on something. Admittedly that is a little circular but that’s how it all works.
Thanks. And what does it mean to have a dependency on something? When I think of having a dependency, I think of people being addicted to drugs or banks depending on big money handouts from the government, or whatever.
For example, we would write
“The man has a dependency on heroin”
but would we also write
“The time it takes to drive to work has a dependency on how busy the roads are”
or
“The time it takes to drive to work has a dependence on how busy the roads are”
Take 2. Dependence is the act.dependency is the state
No idea what that means. Still, thanks for trying again.
I very much hope that you would not write “The time it takes to drive to work has a dependency/dependence on how busy the roads are” :))
What ever has become of Plain English?
They are so close as to make no difference really. I’ve been racking my brain on how to explain it. It really is all about the focus of the sentence. XYZ has an [adverb] dependency . XYZ had a dependence on [noun]. In sentence 1 the stress is on the adverb (Drug/Alcohol/Sex/Programming etc.). In sentence 2 the stress falls on the idea of dependence, the noun is reference point and the dependence is probably the more important bit of information.
We could of course get around the whole issue by using active tense: “The speed of the solar wind depends greatly on the earth’s magnetic field.”
This would be my choice. Technical literature is entirely too fond of the passive voice for my taste. Active verbs fix problems like this and make the material more readable in general.
Of course we could easily get around the issue in this case (see the bottom of my first post), but that was just an example to illustrate the point.
You are right about technical literature being too passive. In the so called ‘hard sciences’, people try really hard not to write in the passive voice or in a passive way. Still, there are so many people who just can’t help it.
By the way, the original example sentence was
“The speed of the solar wind has a dependence on the magnetic field.”
which is not in the passive voice. It is still a bit of a passive sentence.
Grinning here…Looks like us lingQers have been so bored with the forums these past few days that we’ve only got dependency and shoestrings to talk about!.. 
As for me, I’ve been away from the computer, enjoying my new good health in the sunshine:)
I’ve been away from the forum, worrying about the solar wind and trivial grammatical issues…
I know! Because your life depends on it, right? LOL
My job has a dependence on the solar wind stuff, and my inflated male pride has a dependence on the pedantry stuff.
…or should I say dependency?
Well, that depends…
I am afraid of losing my independence. I don’t want to rely on other people. I dislike being dependent. Or, at least, I want to minimize the degree of dependence (or dependency?).
I take some dependence(dependences, dependency, or dependencies?) for granted.
You guys aren’t, directly, answering the (only) question being asked in the OP - which was - “Does anybody know?”.
Clearly, the answer is no.
If you want to answer a question, like - “what should the wording be?” - then surely that would have some level of dependency/dependence upon the actual question being asked?