Breakdown of Он не может найти спички, но они ему нужны.
не
not
он
he / it (for a masculine noun) / it (for a neuter noun)
они
they
ему
to him, to it
Questions & Answers about Он не может найти спички, но они ему нужны.
Why is the plural form нужны used here instead of the default нужно?
When using the short adjective нужен (needed), it must agree in gender and number with the thing that is needed. Here, the subject of the second clause is они (the matches). Because они is plural, we use the plural form нужны. The literal structure of this clause is "they are needed to him."
Why does the second clause use ему instead of он?
In Russian expressions of need using нужен, the person who needs something is placed in the Dative case, because the literal meaning is that something is necessary "to" them. ему is the Dative form of он (he).
Is the word спички (matches) in the Nominative or Accusative case here?
It is in the Accusative case, because it is the direct object of the action (it is what he cannot find). Because a match is an inanimate object, its Accusative plural form looks identical to its Nominative plural form.
Why use the perfective verb найти here instead of the imperfective искать?
найти means "to find" (a completed result), which is the specific result he cannot achieve here. If you used the imperfective искать (to search / to look for), the sentence would mean "he cannot look for the matches" (for example, because he doesn't have time to search), rather than "he cannot find them."