Questions & Answers about Þriðji dagurinn er bestur.
Why does þriðji end with -i?
Þriðji is the masculine singular nominative form of the ordinal number “third.” In Icelandic, ordinals must agree in gender, number, and case with the noun they modify. Since dagurinn (“the day”) is masculine singular nominative, the ordinal takes the -i ending: þriðji.
Why does dagurinn end with -inn?
The base word is dagur (day). Adding -inn makes it definite (“the day”). In Icelandic you don’t use a separate word for “the,” but add a definite suffix. So dagur → dagurinn = “the day.”
Why do we say er bestur instead of just er best?
Bestur is the strong superlative form of the adjective góður (“good”), matching masculine singular nominative. In predicate position, adjectives still agree with the subject’s gender, number, and case, so you need -ur on bestur. Simply best would be indeclinable and is not correct here.
Could we say þriðji dagur er bestur without the -inn on dagurinn?
No. When you use an ordinal (like þriðji), the noun must be in the definite form. Omitting -inn would make dagur indefinite (“a third day”), which doesn’t match the meaning “the third day.” So you must say .