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While "voici" translates to "here is" (or "here are"), as a native French speaker, I've never heard anyone actually use "ici est" or "ici sont" (the plural form). It's just bad sentence structure. They're not quite interchangeable. I wouldn't say "voici" is an abbreviation of, or a contraction for, "ici est" or "ici sont". I'd call "voici" a better word to use where you'd otherwise try to use "ici est" or "ici sont". There's no concern for singular or plural with "voici".
While I can give examples, I can't provide the "why". I don't have a background in that sort of thing. It just is.
(I'm skipping the accents in the following - call me lazy; I don't have the keyboard mapping)
"Voici les faits" = "here are the facts". You wouldn't say however "ici sont les faits".
"Voici la verite" = "here is the truth". Again, you wouldn't say "ici est la verite".
There is no real syntactic difference between "voici" and "voilà". Both may be used to introduce the presentation of something. When a single of them is used, they have the same meaning. In a sentence where you would need to present two disting things, they are often used to denote the distinction.
Example: "Voici Eric, et voilà son frère Marc." => "Here's Eric, and there his brother Marc."
There are two other words which act the same way: "ici" et "là", which can be (roughly) translated to "here" and "there". "Ici se trouve Big Ben, et là la Tamise." => "Here is Big Ben, and there the Thames."
"I'm neither for nor against, on the contrary." John Middle
I'm a native French speaker (French Canadian), and have always had good grades in French while in school. While I have a bit of a knack for spotting common mistakes, I find I rather suck at explaining why they're mistakes as I have no ability to explain grammatical rules such as they exist. I think like a software developer, and I would have a very hard time coming up with any sort of algorithm to do anything with sorting out proper grammar--I wouldn't know where to begin.
I understand your situation completely. I am a native English speaker from England (although now living in the colonies (US)) and have always prided myself on my correct English grammar, spelling and pronunciation. I am usually sought as the source of correct answers in my office and amongst my friends whenever a dispute on "correct English" comes up.
However, why exactly what I say is correct I can never explain using all those "future perfect, pluperfect, etc." words I might once have learned in school (many, many decades ago)- it just is, and somehow I know it, and everyone also accepts it once I state it is so - so it must be!
- I would love to change the world, but they won’t give me the source code.