I'm confused as to why "He cooks on his own" is accepted and "He cooks for himself" is not (unless that was an oversight). They both mean the same thing to me in English (for example, a single man who cooks all his own meals). Since the verb is in an imperfective form, this seems to be talking about cooking in general, not a particular meal that he cooked on his own. Also, "He thinks for himself" was accepted as a translation for "Он думает сам." If Russian speakers think "He cooks for himself" should be accepted, I'll report it next time.
At first I thought it should be accepted, but after reading these conversations, I do think there is a subtle difference.
Imagine there is a dinner party. The guests finish their meal. Next we have this description: - "The host cleared the table by herself"
This suggests (and perhaps emphasises) that nobody else assisted her. What about this line? - "The host cleared the table alone"
Without further description, it is a bit ambiguous. It could mean the same as above or it could mean that everyone had left and she was on her own.
You can write it more clearly and dramatically:
- "The host cleared the table, alone." or
- "Alone, the host cleared the table."
This makes it clear that everyone has gone and she is on her own.
Your loss. English is a rich and expressive language. You can say exactly what you mean with great subtlety and elegance.
Situation: John and Susan are at home...
- "John cooks for himself" (he does not cook for Susan)
- "John cooks by himself" (Susan is not helping with the cooking)
- "John cooks alone" (neither Susan nor anyone else is with John in the kitchen)
- "John alone cooked the meal" (the writer emphasises that John prepared the meal without any help, suggesting that the lack of assistance is remarkable - e.g. perhaps John and Susan had a fight so they didn't share this activity as they normally would, or perhaps this is a noteworthy accomplishment for John, a special meal for Susan)
If you mean, "He is alone while cooking", then I don't think so, based on other comments here. The sentence appears to mean that he is not team-cooking, he is cooking without assistance. There could be people in the kitchen with him. So, if you mean unassisted, then by himself should be correct.
Also, it doesn't mean "cooking for himself" - he could be cooking a meal for others. See the other discussion here. You could be right, but it doesn't appear so.
I believe technically it is correct. At least to me it is. Lets' try to translate from English "he cooks alone" to Rus, it would probably be :" он сам готовиь" or " он готовить сам". So it is correct, and that is why I reported it. On the other hand, if the sentence had a bit of context, it would have been easier for us to translate.... like is he a brokenhearted drunk cooking alone in the gloomy kitchen, or is he cooking by himself a special dinner for his "подруга" ......:)
The difference between the two is nuanced in English. If we say "He prepares that himself," what we mean is that he prepares that "by himself," that is, without assistance. "That" is the direct object of "prepared" and "himself" is an adverb. If we say, "He prepares himself," it is reflexive, meaning it was himself that he was preparing ("himself" is now the direct object of prepares). As I understand it (and my study of Russian was limited to 2 years), "Он готовит сам" corresponds to the first usage (where the direct object "ужин" or "едy" is implied), while "Он готовит себе" corresponds to the latter.