Don't make the mistake of thinking that 'still' and 'yet' are synonyms - they are not. * 'Still' describes a situation which is continuing * 'Yet' is used with questions and negatives and refers to an event which we expect to happen. We use 'yet' to either ask whether it has happened, or say that it hasn't happened so far. Take a look at these examples. He's still at school = He hasn't left school yet I'm still working = I haven't finished my work yet The shops are still open = The shops haven't closed yet He is still sick = He hasn't got better yet. In each pair of sentences, the same situation is described, but from a different angle. The first sentence describes the situation which is still continuing, while the second says what has not yet happened. I hope that makes sense.

This is really tricky. According to the Brits " ‘Yet’ is used to talk about something which is expected to happen... ‘Still’ is used to talk about something that hasn’t finished." So in your example "he is still working" implies that he is physically at work, or is actively working at the present moment. You cannot say "He is working yet" because you are making a statement about what is currently happening and then adding the expectation that it will happen, and it is impossible to expect something to happen that is currently happening. Does that help at all? Try going here: https://learnenglish.britishcouncil.org/en/grammar-reference/just-yet-still-already

You can say "he is working yet" but that sentence, as Su.KI writes, is probably in response to a question such as, "Is he working?" or "Has he lost his job?" The respective answers being, "Yes, he is working" or "No, he is working yet." For the sake of clarity, I would use the word still in both sentences rather than yet unless I want to suggest his status is about to change. If his status is about to change, I would use the word yet. For example, "He is working, yet he may be laid off at the end of the month." In this sense, yet carries the connotation of the word but. I hope this helps.

The easiest way not to make mistakes is to remember this: 'Yet' can only be used in this sense with questions and negatives.