At 2:28:56 PM on Sunday, July 5, 2009, nikolai_sandbeck
wrote:

> Hej, i got two examples here of time, the first one is
> dativ used (dögum):

> Þat var á dögum Haralds konungs ins hárfagra, Hálfdanar
> sonar ins svarta, at sá maðr kom skipi sínu til Íslands í
> Breiðdal, er Hallfreðr hét.


> and the second one is accusative used (nótt):

> Ok eina nótt dreymdi hann, at maðr kom at honum ok mælti:
> "þar liggr þú, Hallfreðr, ok heldr óvarliga. Fœr þú á
> brott bú þitt ok vestr yfir Lagarfljót. Þar er heill þín
> öll,"


> Which one scould i use? :s

Non-prepositional expressions of time normally use the
accusative, as in your second example.

> Is the dögum in dative only becuase of á?

Partly, but <á> can take either the accusative or the
dative, and both do occur in expressions of time. According
to Michael Barnes (A New Introduction to Old Norse), <á>
tends to trigger the accusative when the noun is accompanied
by the definite article:

<á várin> (acc. sing.) 'in the spring';
<á laugardaginn næsta> (acc. sing.) 'on the next Saturday;
<á várum> (dat. pl.), literally 'in springs', but meaning
something like '(in) every spring' and often
translatable in English as 'in the spring';
<á því sumri> (dat. sing.) 'in that summer'.

Brian