The other day I posted a picture of some food on Facebook, and I noticed that all of my Japanese friends were saying 「おいしそう」. I made a good guess to what it meant, but I wasn't certain what exactly they were saying. I've seen this stem+そう with other i-adjectives too, such as 楽しそう, but none of this is covered in any of my Japanese books.
What exactly is this? Is it slang? Can it be used with na-adjectives or nouns too? If so how? Thanks! :)
[See this question, which deals with the same pattern when used with verbs. I'll adapt my answer from that question to answer yours.]
-そう after the stem of a adjective means "looking/sounding as if ___." おいしそう means "it looks as if it will be delicious." It is similar to constructions like おいしいみたい or おいしいよう, but -そう emphasizes evidence of the senses rather than general "seeming."
Contrast it with おいしいそう, which means "it is said to be delicious."
You can use -そう with verbs, adjectives, and some na-adjectives, but not with nouns. Here are some na-adjective examples:
You can also use the -そう phrase itself as a na-adjective:
It seems ...
For instance
It is not slang, it is grammatically correct.
Detailed explanation: http://www.guidetojapanese.org/similar.html#part4
