The good old nonsense phrase of foreign languages is Monty Python's classic "My hovercraft is full of eels".
Accordingly in Japanese one of the first things I learned was "私のホバークラフトはうなぎがいっぱいです".
However, today I have been told that this is wrong, that I should in fact be using "私のホバークラフトはうなぎでいっぱいです"
Can anyone shed some light on this? Does the first one truly make no sense (as far as the sentence can make sense anyway)?
Why is it で and not が?
私のホバークラフトはうなぎがいっぱいです Eels abound in my hovercraft.
私のホバークラフトはうなぎでいっぱいです My hovercraft is filled with eels.
Thus, the latter sentence should be used to express your original English. I've found this page translates it in the same way, too.
いっぱい literally means "full", but only used in this sense with the construction A が B でいっぱい "A is filled with B" or "A is full of B". It has another usage X が Y にいっぱい, in turn means "X abounds in Y" or "X is everywhere in Y".
As a native speaker, I can't help but imagine a hovercraft fully decorated with eel-motif carvings and accessories with ホバークラフトはうなぎがいっぱい, before I reach the correct interpretation.
If you'd like to rephrase it with eel + が, you'd say:
私のホバークラフトはうなぎがいっぱい入っています
But it doesn't necessarily mean that hovercraft is literally full, while うなぎでいっぱい always does.
私のホバークラフトはウナギで一杯{いっぱい}です
This sentence takes the particle で because で indicates the location of the eels (the hovercraft). で is used to mark a location instead of に because, in this case, 一杯｛いっぱい｝ is an adverb which is modifying the copula verb です. で means/translates to in when used with a verb, for example,
日本語で話す To talk in Japanese.
You can use が, if you wish, and say something like:
私のホバークラフトの中にたくさんウナギがたくさんいる There are many eels inside my hovercraft.
In this case, you can use が because たくさん (many) is an adjective modifying the noun (eels), as opposed to an adverb 一杯 (fully) modifying the auxiliary verb です.
With regards to the second part of your question, I can assure you the original sentence using が makes complete sense. It's just a minor grammatical mistake, people will still understand you. (Interestingly enough, you can also easily drop が or で in this sentence, and remove です and it will have the same meaning. You can do this because certain particles in casual speech (and sometimes even formal speech, see 時に vs. 時) can be removed without altering the meaning at all. The particles は、が、に、へ、を all can be removed in casual speech.)
In simple terms, が is a subject marker. So your first sentence parses out to something like, "As for my hovercraft, the eel(s) is (are) full."
Meanwhile, で can be used as a marker for the instrument by which something happens, a bit like English "by" or "with". 手で作る is to make something by or with your hands. So the second sentence parses out to, "As for my hovercraft, it is full with eels → it is full of eels."
