Which preposition(s) is / are correct in the following example?
We contacted the college authority over / on / by Skype.
Technically you can use quite a variety of prepositions with the word Skype. For instance on, in, over, by, with, through, and via.
But most people prefer "on Skype" as it is similar to "on the phone". However, in technical documentation and in formal speech I often hear "via Skype".
As for the other prepositions, they are used less often but sometimes in a different context.:
The most common usage is to use the preposition on in the example you have provided although the other prepositions are not incorrect. This area is evolving, and preposition usage can often be varied, depending on local usage and the fact, as stated by Joi de Vivre, that English is fairly flexible/lax in its use of prepositions.
As I expect you are aware, Skype is also commonly used as a verb –– We Skyped the college authority.
We contacted them over Skype. - GOOD
We contacted them on Skype. - GOOD
We contacted them by Skype. - MAYBE. Sounds weird to me but also makes sense if you think about it for a couple of seconds. I'd recommend using one of the other phrases.
We contacted them via Skype. - GOOD
We contacted them in Skype. - BAD. Sounds weird. Gives the impression of shrinking yourself and crawling into the messenger. Hahaha.
We contacted them at Skype. - BAD. Sounds weird. Gives the impression of contacting them at Skype's headquarters building, rather than via the Skype messenger.
over Skype, which is one of the best answers here, was lowest in the Google results, while
in Skype and
at Skype were ranked higher. This is why Googling is not always the best way to answer language questions.
Based on Google the most common preposition in this specific context is "on". However, I think the question should be expended with the question about the options "in" and "at", since they are also variants that people may use sometimes.
The searching on Google based on these sentences:
"contact by / in/ on/ over"
"contact me by / in/ on/ over"
The results show the frequency of the prepositions in Google as follow:
1st place: the preposition on.
2nd place: the preposition by.
3rd place: the preposition in.
4th place: the preposition at.
5th place: the preposition over.
But be aware that the preposition "on" is very dominant in use (113K results) compared to "by" (20K results) and "in" (17K results) while "at" and "over" has a very few results (4.4K and 1.9K correspondingly) compared to all of them.
In addition, I think that Cambridge dictionary supports the most frequent preposition for that "on":
Most answers to this question seem to be assuming that the object of the preposition dictates which preposition is the most appropriate to use. The object matters a little, but the verb in the sentence is usually much more important for choosing the best preposition. English is pretty lax about prepositions compared to some other languages, so none of the proposed prepositions is necessarily incorrect. However, I would say that the best prepositions to use with the verb "contact" are usually "by" (a method), "on" (a platform), "in" (a location), or "at" (other types of locations).
Here, where you are using Skype by itself, "on" sounds more natural, because Skype is a platform. But Skype is also a method for contacting someone. For example, if you used it in a list of other methods for contacting you, you'd want to use "by," as in, "You can contact me by phone, email, or Skype."
Examples of contact with these various types of prepositions:
Contact me on Facebook. (platform)
Contact me by phone. (method)
Contact me in Rome. (location)
Contact me at home. (location)
Note that with "on," "in," and "at" the prepositional phrase is saying where you want to be contacted. With "by," the phrase is saying how you want to be contacted.
Contrary to what others have said, I don't think that the prepositions "over" and "through" go very well with the verb "contact." The meaning of the verb doesn't lend itself well to the meanings of these prepositions. In the given example, "over" is actually ambiguous. If you tell me you contacted the authorities over Skype, I actually won't know if you spoke to them using Skype or if you talked to them on the phone or in person or in some other way about Skype.
In the given example, over.
Skype is a service/application, so over is the best choice of the three.
I would also point out that through or using work well in other situations too.
"You can contact me using Skype." "You can call me through Skype."
However when referring to your use of Skype as a platform it would be on.
"You can find me on Skype."
"Add me as a friend on Skype so that I can call you."