Dear language professionals,
What are grounds for using shortish phrase "Life vest under your seat" on the warning sign on the planes.
Is it stylistically caused? If this style allows main verb omission? Or it is just an unmotivated verb omission?
It's a feature of a lot of texts exhibiting frozen style. It's a highly predictable and regular style found in newspaper headlines, signs, notices, instructions, lab reports, technical reports, legal documents, public declarations and so forth. In this kind of style in certain text-types, auxiliary verbs are regularly omitted when we can recover them from the context. So are articles and other determiners, as well as pronouns, prepositions and quantifiers. These words are highly predictable from the context and so this causes very little problem in terms of communication:
The one thing that all these types of text have in common is that they do not have a lot of space to work with.
In general, frozen style does not easily permit the omission of lexical, or main verbs. Note that although BE is the only verb in many sentences, it always functions as an auxiliary verb, and is practically always omissible in frozen style. This is because, it is argued, BE has no discernible meaning. This is also why many languages have no (everyday) verb for BE at all.
The elements of frozen style are not by any means random, and have been studied extensively in the fields of discourse analysis, pragmatics and syntax.
[However, I'm not an expert in this area, and so can't fill you in on what they found out!]
I learned a similar style of writing in my 3rd level college "Technical Writing" course. Technical Writing is commonly used in instruction manuals and in industrial documentation. These are areas where it would be inappropriate to use the same style of language as if you were writing a "Dear John" letter. It is used to convey ideas quickly without flowery language that could obscure precise meaning. You may have come across instruction manuals which are so badly written that it takes hours to figure out how to operate something. Technical Writing condenses the manual to its unmistakable essentials, considerably shortening the documentation, and reduces potentially deadly mistakes. Though the style seems stilted, the document becomes much easier to understand. The manuals from foreign manufacturers would benefit greatly if they hired some technical writers. Sadly they cheap out on this score.
Articles, prepositions and auxiliary verbs are often omitted from the newspaper headlines, warnings etc.
It's not "redundant". That implies extra word meaning the same thing. If anything, it's the opposite of redundant.
The "grounds" are not grammatical, they are economical. In a warning/advisory sign like that, you need the minimum wordage to convey the message.