Thank you

The verb must be in second place (except in subclauses and questions). enligt honom is an adverbial and when we put it first, we have no choice but to put the verb next. If we had put skärpet first, it would be Skärpet är grönt enligt honom

I agree with you I did it like that

It’s also accepted.

*skärpet
However, you should really try to keep word order the same as much as possible when translating here. Swedish and English work much the same so there is really no need to change word order in most cases.

That would also be Är skärpet grönt? Questions are created by putting the verb before the subejct. (if there's a question word like var 'where' etc it goes first of all, but nothing else can go before the verb).

Non-question main clauses, like the one above, always have the verb in the second place. Here, the sentence starts out with an adverbial phrase "enligt honom", so the verb must go right after that.

Sometimes people will tell you that questions are created by 'reversing' word order, but that is not a good description, since it presupposes that the subject should go first in normal sentences. However there is no such rule, the rule just says that the verb must go second (in main clauses that are not questions).

No. Read the above comments. The verb (är) must take the second place in the sentence. This is called the V2 rule.
First place = Enligt honom
Second place = är
Third place will always be the subject (in this sentence = skärpet) if the subject is not in the first place.

Adjectives change form according to the word that they are describing.

For indefinite nouns in the singular eg en katt - a cat, ett barn - a child etc. the adjective has an ett or an en form which correlates to the noun in question. Typically the ett form of the adjective has a "t" on the end of the en form but they can be a little irregular.

So using the word green the above nouns would be:
En grön katt
Ett grönt barn

In the indefinite plural form the adjective has a different form. Typically this takes an "-a" on the end of the en form. So in this case: several green houses - flera gröna hus. Plurals take the -a ending regardless of gender.

In addition there is the double definite form. Swedish has an oddity in that when a definite noun is used with an adjective a separate article is used in addition to the definite form of the noun. When we use the double definite form the adjective takes the definite form which is also typically the en form with a "-a" on the end. eg. the green animal - det gröna djur.

Note that definite nouns take the "indefinite form" when the adjective follows the noun. eg. The turtle is green - Sköldpaddan är grön. Huset är blått. Hundarna är vita.
The definite noun only takes the definite adjectival form in the double definite structure as described above.

So to summarise:
Singular en word: a green dog - en grön hund
Singular ett word: a green apple - ett grönt äpple
Plural of either en/ett word: turtles are green - sköldpaddor är gröna
The double definite of either en or ett word: the green lamp - den gröna lampa
Where the adjective follows the noun, it takes the "indefinite" form: the shirt is brown - skjortan är brun

More is explained in the first lesson on adjectives when you get to that. (Edit: Also see my additional comment below to Martin re: attributive vs predicative adjectives which further clarifies this comment.)

So Swedish tends to have a rather strict word order for main sentences. For a huvudsats (main sentence) some basic rules are as follows:

1. First place (nb is often the subject but can be a TSP adverbial or is often a whole subclause too! Also note that word order in subclauses is slightly different.)
2. The verb... ALWAYS. The second place takes the verb that sets the tense ie the finite verb. This is the V2 rule that you see written everywhere and applies to pretty much all sentences except questions and commands.
3. The subject if not in first place
4. The satsadverbial eg inte, aldrig etc
5. The infinitive verb/further verbs
6. The object
7. TSP adverbial - specify the time, place or other setting/situation (I honestly do not know exactly what "S" is meant to stand for precisely!

In this case the main sentence (huvudsats) is the whole sentence as above: Enligt honom är skärpet grönt, and the adverbial is Enligt honom. So the first place of the sentence is taken up by the adverbial "enligt honom" and the second place is (as always) the verb är.

Hope that helps a little?

Read the comments above. There is some thorough explanations.

Again, I think I've answered my own question. Can I move the "according to him" part to the end of the sentence?

Does this work: "Är skärpet grön, enligt honom?"

grön is a regular Swedish adjective, so it follows the common pattern of

• singular indefinite en-word = base form
• singular indefinite ett-word = base form + t
• both plural forms = base form + a
• all definite forms = same as plural
• optional mascular singular definite form = base form + e

Have a look e.g. here for a conjugation table: https://en.wiktionary.org/wiki/gr%C3%B6n#Conjugation

bälten is the plural - "belts".

I know it's just a typo, but "word oder logic" seems to sum the issue up nicely. :)

Please have a look at the above comments - this question has been answered before.

Sentences do not necessarily have to be true to be useful in the course.

I am pretty sure that this has been covered above but sometimes the comments don't all show up so I will answer in brief... Essentially this is the V2 rule. In a main/statement sentence the verb must always be in second place. Enligt honom is in first place, so the verb är must take the next spot. The sentence could be rearranged to read "Skärpet är grönt enligt honom" but note that the verb remains in second place, this time after the subject. (Also note that that would not be a correct answer here because it does not follow the structure of the English sentence.)

I recommend coming back on desktop and reading the comments above for a more complete explanation though. There is a reasonably good summary on sentence structure above that I wrote another time when I was feeling enthusiastic!