http://en.wikipedia.org/wiki/Swedish_grammar
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Articles and definite forms
The definite article in Swedish is mostly expressed by a suffix on
the head noun, while the indefinite article is a separate word preceding
the noun. This structure of the articles is shared by the Scandinavian
languages. Articles differ in form depending on the gender and number of
the noun.
The indefinite article, which is only used in the singular, is "en" for common nouns, and "ett" for neuter nouns, e.g. en flaska (a bottle), ett brev (a letter). The definite article in the singular is generally the suffixes "-en" or "-n" for common nouns (e.g. flaskan "the bottle"), and "-et" or "-t" for neuter nouns (e.g. brevet "the letter"). The definite article in the plural is "-na", "-a" or "-en", depending on declension group, for example flaskorna (the bottles), breven (the letters).
When an adjective or numeral is used in front of a noun with the
definite article, an additional definite article is placed before the
adjective(s). This additional definite article is det for neuter nouns, den for common nouns, and de for plural nouns, e.g. den nya flaskan (the new bottle), det nya brevet (the new letter), de fem flaskorna (the five bottles). A similar structure involving the same kind of circumfixing of the definite article with the words där (there) or här (here) is used to mean "this" and "that", e.g. den här flaskan (this bottle), det där brevet (that letter) as a demonstrative article.
The five declension classes may be named -or, -ar, -er, -n, and null
after their respective plural indefinite endings. Each noun has eight
forms: singular/plural, definite/indefinite and caseless/genitive. The
caseless form is sometimes referred to as nominative, even though it is used for grammatical objects as well as subject."