Is, sem, and double negatives

 [Originally posted on 2019-07-19 on the Duolingo Hungarian for English speakers forum by jzsuzsi. ]

is

In Hungarian, is means too or also. We place is right after the word it refers to.  

Examples:  

I, too, like horses = Én is szeretem a lovakat. 

I like horses too (stress on "I" and "too" in speech) = Én is szeretem a lovakat.

I like horses too = I like horses (in addition to something else that has already been mentioned)   Szeretem a lovakat is.

Én is okos vagyok = I am also smart. (and someone else is smart as well)

Én okos is vagyok és szép is. = I am smart and beautiful too.

This word order rule, "We place is right after the word it refers to." is really important, mainly because it is different from English. In English you can just put too at the end of the sentence, and the meaning is ambiguous. In Hungarian, it is never ambiguous.

Some tips:

• Never put is at the beginning of the sentence. As we have seen, "is" refers to the word right before it. If it is the first word of the sentence, what does it refer to? Nothing. That does not work.
• Placing "is" after the verb is possible (but rare)

Szeretlek is meg nem is.  = I love you and also don't love you.

Látom és hallom is a filmet. = I see and also hear the movie.  

These examples are relatively rare, and do not appear Duolingo Hungarian course.
As a survival tip on Duolingo, do not put is after the verb. 
As a survival tip in real life, it is okay to put is after the verb. :)

sem

Sem means neither. It is the negated form of is. 

Again, we place sem right after the word it refers to.  

I also don't like horses  (someone else also does not like them) = Én sem szeretem a lovakat.

I do not like horses either = I don't like horses (in addition to some other animals)   Nem szeretem a lovakat sem. / A lovakat sem szeretem.

I do not like horses either = I don't like horses (in addition to not liking riding them)    Nem is szeretem a lovakat.

Not as simple as the examples with is, but here I can say the same tips. 

• Most of the time, do not put sem at the beginning of the sentence, since "sem" refers to the word right before it.  (Well, there are some exceptions, but those are rare.)

• Do not place it after the verb. Here,  "szeretem sem" is impossible, we would use "nem is szeretem" instead. 

 Nem látom és nem is hallom a filmet. = I do see and also do not hear the movie.

Double negation

You know nothing, Jon Snow!  -  Nem tudsz te semmit, Havas Jon!

Hungarian uses double negatives.  In English, we say "I do not see anything", while the Hungarian version would be literally  "I do not see nothing." - Nem látok semmit.  This is considered bad grammar in English, but perfectly fine (and mandatory) in Hungarian. 

When the following pronouns are used in a negative sentence, we usually get a double negative. Pronouns in question are:

senki nobody

semmi nothing

sehol (sehová, sehonnan)  (to/from) nowhere

soha  never

When the above negative pronoun comes AFTER the predicate (verb in this context), we have an N-S pattern. That is, we use Nem and then Senki.

When one of the above negative pronouns comes BEFORE the predicate, we have an S-S pattern. That is, we use Senki and then Sem.  But in this case, using Nem instead of Sem also works.  (Using sem is more natural.)

What's more, we can have a triple negation, with an N-S-S pattern.  
Caution: earlier we learned that sem alone means neither.  But semmi sem and semmi nem  (or senki sem and senki nem) are equivalent. 

Nem tudsz semmit sem. - You don't know anything.

Nem ismerek senkit sem itt.  - I don't know anyone here.

Back to the "You know nothing" example, all of these are possible in Hungarian: 

Nem tudsz semmit. 

Semmit sem tudsz.

Semmit nem tudsz. 

Nem tudsz semmit sem.

Note: I used Hungarianreference as a source, but it also contains some mistakes, so I don't link it here. 

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Extra info / exceptions for the above:

Sem

I said do not start the sentence with "sem". But in some cases, it is possible, and follows a pattern like Sem X sem Y nem .... 

Sem utódja, sem boldog őse,
sem rokona, sem ismerőse
nem vagyok senkinek,
nem vagyok senkinek. (Ady Endre)

I am no heir, no proud ancestor,
I have no friend, no brother, sister,
I have never belonged,
I have never belonged.

(Translation by Peter Zollman, https://www.babelmatrix.org/works/hu/Ady_Endre-1877/Szeretn%C3%A9m%2C_ha_szeretn%C3%A9nek/en/1958-I_want_to_be_loved )

A mentőállomás súlyos munkaerőhiánnyal küzd, sem elég mentőápoló, sem elég gépkocsivezető nincs.

The ambulance station suffers from a severe shortage of manpower, there are neither enough paramedics nor enough drivers.

So we can see the pattern was  Sem X sem Y nem .... / Sem X sem Y nincs ...