I really think that I should use "the baby can't eat BY himself" to make it clear, but my friend argues that the first phrase would still be correct and mean the same thing as the second phrase. But I am still not sure, "can't eat himself" just sounds wrong to me. By the way, me and my friend are not native english speakers.
Learn English – Is it grammatically correct to say “the baby can’t eat himself” meaning that the baby can’t eat without help
grammar
Best Answer
It should be, "The baby can't feed himself."
While most people could properly infer your meaning if you said, "The baby can't eat by himself," that sentence could also mean that for some reason, the baby needs to eat with other people in attendance, not necessarily because he is incapable of feeding himself.
You are correct that, "The baby can't eat himself," is absolutely the wrong thing to say. This sentence means that the baby cannot consume his own body as food. This is a very odd thing to say.