Is it a big mistake when I say:
"Summer of 2009 with you was so magic" instead of "The summer of 2009 with you was so magic."
Is the first sentence a wrong usage (between native speakers).
It is probably more common to say "THE summer of 2009," but it is far from a big mistake. I don't think anyone would particularly notice one way or the other.
A more arresting error is "so magic" This should be either
> "so magical" or "totally magical" (adverbs)
> "sheer magic" or "pure magic" or "total magic." (adjectives)
F.i. if I want to compare summer with winter in general, should I use the definite article?
"Which time of the year do you prefer? Summer or winter?" or "Which time of the year do you prefer? The Summer or the winter?"
I mean is it a big mistake? Do english speakers use the form without the article?
There is probably a slight tendency to omit the article in this case, but using it is not an error. No one would notice one way or the other.