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"Jemand ist willkommen" would mean "somebody is welcome". Both "jeder" and "alle" can mean "everyone", but there's a subtle difference between them, which is that the former addresses every member of the group as an individual, while the latter addresses the group as a whole. It's the same thing with "keiner" and "niemand". Both can mean "nobody", but the latter is a more general statement, while the former addresses each member of a specific group.
Actually, "is welcomed" isn't past tense. it's present perfect tense. See here: http://www.englishpage.com/verbpage/presentperfect.html , under Topic 5 (Multiple Actions at Different Times). When you say "everyone is welcomed," let's say, in a restaurant, it means that for an unspecified amount of time, every time someone goes in, they get greeted, or there are some actions employed which make that person feel welcome. On the other hand, "Everyone is welcome" is simple present tense. It means, for this time, anyone can come to the restaurant. They are free to come, but they won't necessarily be greeted. Your examples for this are right ("Everyone is welcome at any time" or "Everyone is welcome to join us"), it's just the 'past tense' thing that I wanted to correct.
Sorry for that grammar lesson. -_-'
I think "jeder" is the default word so to speak, it's not the inflected form of jed-
Because if you search wiki for jedes or jedem e.g. https://en.wiktionary.org/wiki/jedes it will tell you it's the inflection of "jeder".
So I guess when there's no noun we use the default word "jeder".
So there's jed- which gets inflected much like kein-
And then there's jeder and keiner which are actual words (not inflected forms).
Will be great if someone says if this is correct or not :)
Depends upon the context. I'm not exactly sure, but since Jeder is technically the noun in this sentence, it wouldn't be every, however if it were to say something along the lines of Jeder Mann ist wilkommen, then it would be every as there is another noun after jeder. If I'm wrong please correct me so we can all learn :)
"Everyone" (Jedermann) can only be used to refer to persons. It is, therefore, of a higher register and usually only used when a broad, all-encompassing term is needed; a law might state "Everybody (Jeder) is obligated" = "Everybody must", eg But even then "everyone" could be used. Feminists want to tell you that every man excludes women and should be avoided for that reason alone.
Think I've figured the Alle vs Alles v Jeder bit.
"Alle Kuchen schmecken lecker;" - 'All cake tastes delicious.' In this context, you're declaring that literally all cake, as an absolute, tastes good. Alle means "all" in a broad scope; making something vast, an absolute but defined subject. It also looks like the subject it modifies has to be plural.
"Er hat Alles, aber ich habe Kuchen!" - 'He has everything, but I have cake!" or "Das Alles" for 'All that.' It looks like this doesn't address any specific item or group, but the english "everything" seems to be a direct meaning in most cases.
"Jeder Kuchen schmekt lecker;" 'Every (one)/each cake tastes good.' This implies that you're referring to all of a group of cakes, but as individuals, part of a bigger whole.
I think the choice between alle and jeder comes down to the intent of the tone, "Jede Mann, Frau und Kind" or 'Every man, woman and child' sounding more intimate and humanizing than "alle Männer, Frauen und Kinder" or 'all men women and children.'
Then there's "ganze..."
"Essen Sie nicht den ganzen Kuchen auf einmal;" "Don't eat all the cake at once." Ganze/n seems to mean "all of" or the "whole" or the "entire," summarizing the scope of a specific thing being addressed, like 'all night' or 'the entire time' or 'the whole enchilada.'
Jeder and ganze seem to be subject to regular conjugation depending on the gender of the noun they modify (or are understood to modify) and also the case of the sentence.
Sorry if there's errors, still learning.