How much does knowledge of linguistics help with learning foreign languages?

[FlatAssembler]

So, I have two related questions for you. I think no previous knowledge of linguistics is necessary for the discussion.

1. Does the knowledge of regular sound changes help with learning a foreign language related to a language you already know?
For instance, let's say you know English very well. Does it help you with learning German to know the following and similar rules (they apply to the Germanic words and very early Latin borrowings):
English "t" corresponds to German "z", which is read "ts", in the beginning of a word (two-zwei, ten-zehn, tooth-Zahn, tongue-Zunge, twig-Zweig…) and after "r" (heart-Herz…), but corresponds to "s" otherwise (water-Wasser, it-es, that-das, what-was…) except after "s", when it corresponds to "t" (star-Stern, stone-Stein…)
English "th" corresponds to German "d" (three-drei, that-das, thick-dick, mouth-Mund, death-Tod…)
English "v" corresponds to German "b" (seven-sieben, give-geben, live-leben, have-haben…)
English "d" corresponds to German "t" (desk-Tisch, word-Wort, god-Gott, ride-reiten…), but English "nd" corresponds to German "nd" (wind-Wind, hundred-hundert…)
English "oo" corresponds to German "u" (book-Buch, foot-Fuss, too-zu…)
English "one" and "ome" corresponds to German "ein" (pronounced ahyn) and "eim" (pronounced "ahym"), respectively (one-ein, stone-Stein, alone-allein, home-Heim…)
English "ou" corresponds to German "au" (house-Haus, out-aus, show-schauen…)
English "ea" usually corresponds to German "o" (ear-Ohr, east-Osten, easter-Obster, bread-Brot, bean-Bohne, death-Tod…)
I believe this was enough for anyone to get the basic idea.

2. Does knowing an archaic language from some family help with learning modern languages from that family?
For example, I've heard that, if you know Old Church Slavonic, you can basically understand all Slavic languages. Is that true?

[Aoi Magi]

As far as I know, it varies from person to person, but our human brain works through association so learning languages gets easier if you already know a language similar to it and an ancient root of the language you are trying to learn obviously will have a lot of similarities.

As for knowing those rules, I personally don't find them very useful. While using a language in practice we never think of the actual rules rather we just say whatever sounds right to the ear, and for me just practising with a native speaker without bothering about grammar and such seem a lot more useful.

[Alex K]

Well, being German, the above relationships made learning English much easier, but not because I knew the principles. I don't know whether I would have profited from having the abstract knowledge about the rules. Maybe...

[FlatAssembler]

Well, it might help you recognize the tricky cognates. You know, death-Tod or too-zu or the likes. The words don't look similar at all. Yet, if you analyze the English word phoneme by phoneme, d-ea-th, and apply the rules, you can correctly predict that the German word would be T-o-d.
Or the likes of it-es or thick-dick. In the first word, the English cognate, by the basic rules, obviously ends with a t. Though it's kinda tricky, if not impossible, to predict from an English word whether the German word has an i or an e (I don't know enough about Proto-Germanic phonology to explain exactly why). Nevertheless, the rules can still help a little even with those words.
But, unless you know exactly what you are doing, those rules might lead you right in the wrong direction when you try to decipher a German text.
In the worst case, they can just help you remember the words you already know, the same way knowing how an English word is pronounced and some basic spelling rules helps with remembering how it's spelled, right?
My native language is Croatian, BTW.

Not understanding what types of rules apply to actually related languages appears to be the root of many, if not most of the, pseudosciences in linguistics.

[Astreja]

I don't think that knowledge of the nuts and bolts of a language is necessary to become reasonably fluent, although it would definitely help you do higher-level writing in that language. Think back to childhood, when you learned your first language: Unless you lived in a very odd household, chances are someone didn't lecture you on phonemes and declensions and such -- they just spoke to you, and eventually you made a transition from speaking to writing.

Personally I think that immersion (travelling; watching and listening to shows in a language, reading websites in a language) is the best way to learn to speak with native speakers.

[FlatAssembler]

Think back to childhood, when you learned your first language: Unless you lived in a very odd household, chances are someone didn't lecture you on phonemes and declensions and such -- they just spoke to you, and eventually you made a transition from speaking to writing.

I agree with you on that. Learning syntax and morphology in details doesn't really help you speak a language grammatically, and it could actually be counter-productive. But, if you already know a closely related language, knowing the sound changes might help you remember the vocabulary.

[Javaman]

So, I have two related questions for you. I think no previous knowledge of linguistics is necessary for the discussion.

1. Does the knowledge of regular sound changes help with learning a foreign language related to a language you already know?
For instance, let's say you know English very well. Does it help you with learning German to know the following and similar rules (they apply to the Germanic words and very early Latin borrowings):
English "t" corresponds to German "z", which is read "ts", in the beginning of a word (two-zwei, ten-zehn, tooth-Zahn, tongue-Zunge, twig-Zweig…) and after "r" (heart-Herz…), but corresponds to "s" otherwise (water-Wasser, it-es, that-das, what-was…) except after "s", when it corresponds to "t" (star-Stern, stone-Stein…)
English "th" corresponds to German "d" (three-drei, that-das, thick-dick, mouth-Mund, death-Tod…)
English "v" corresponds to German "b" (seven-sieben, give-geben, live-leben, have-haben…)
English "d" corresponds to German "t" (desk-Tisch, word-Wort, god-Gott, ride-reiten…), but English "nd" corresponds to German "nd" (wind-Wind, hundred-hundert…)
English "oo" corresponds to German "u" (book-Buch, foot-Fuss, too-zu…)
English "one" and "ome" corresponds to German "ein" (pronounced ahyn) and "eim" (pronounced "ahym"), respectively (one-ein, stone-Stein, alone-allein, home-Heim…)
English "ou" corresponds to German "au" (house-Haus, out-aus, show-schauen…)
English "ea" usually corresponds to German "o" (ear-Ohr, east-Osten, easter-Obster, bread-Brot, bean-Bohne, death-Tod…)
I believe this was enough for anyone to get the basic idea.

2. Does knowing an archaic language from some family help with learning modern languages from that family?
For example, I've heard that, if you know Old Church Slavonic, you can basically understand all Slavic languages. Is that true?

I'd say yes and yes to your questions.

My follow up question would be... What matters more: phonemic similarities or the underlying syntax and grammar?

My (very limited) understanding of linguistics is that languages are grouped moreso on syntax and grammar than phonetic similarities. Phonetic similarities are more a symptom than a cause. I'm happy to be corrected if I'm wrong on that.

On a side note, I find these kinds of discussions highly interesting. I want to learn more lol.

[FlatAssembler]

My (very limited) understanding of linguistics is that languages are grouped moreso on syntax and grammar than phonetic similarities. Phonetic similarities are more a symptom than a cause. I'm happy to be corrected if I'm wrong on that.

The way languages are proven to be related is by finding simple regular sound changes and finding many examples of them in words that are unlikely to be loanwords (numerals, body parts, basic agriculture…). Sound changes I've listed would be examples. Of course, linguists would try to find as many examples as possible, much more than I did, to make it less likely that those examples are due to chance alone. Grammar can be used to prove language relationships only if you can show that regular sound changes operate in grammatical words (like the conjugation of the verb "be") or, rarely, in affixes (like conjugational endings).
And, yes, I think the schools place too much attention on grammar when teaching linguistics (I also think they are teaching grammar the wrong way, but that's another story), and way too little attention on the laws which govern how languages are related.

[FlatAssembler]

I am currently having a discussion about that on a forum about linguistics (because I suggested that two ancient languages, that mainstream linguistics considers unrelated, are, in fact, related), you can follow it if you want to:
http://linguistforum.com/outside-of-the-...-toponyms/

[FlatAssembler]

Many of you guys have researched pseudosciences, and we are currently discussing there how to recognize pseudoscience in comparative linguistics and etymology. It may be interesting to hear your thoughts.