All these words have similar meanings. The difference usually comes when they are used. For example. Probably is the most common. It is used on an every day basis, and usually used when someone has a strong opinion about the subject or its a more personal matter "I probably won't do my homework." or "I probably won't see her tonight." Likely is much the same as probably. However, it is unlikely you will hear it as much. ;) Possible DOES NOT mean likely/probably. If something is possible it means it could happen. However, just because it could happen doesn't mean it WILL happen. "Can a cat jump?" ... "It's likely." .... "Will robots take over the world one day?" .... "It's possible" There is a big difference. Feasible means it could be possible. Not similar to likely or probably

likely、possible、 probably、feasible The best way to answer your question is to think of a situation where you can use these words. The difference is not based on formal or informal. The difference is based on degree. What do I mean? Let's pretend as if I asked you will you cook dinner tonight. (So to use these words, you generally refer to some future event.) if 0% = no, and 100% = yes, then these words fall in between those two percentages. Possible means some event is going to happen as long as nothing prevents it from happening. Example: Will you cook dinner tonight? Reply: Possible, unless my boss makes me work overtime again. Feasible means you have a desire to do something and you can easily do it. Will you cook dinner tonight? Reply: It's feasible, but I've cooked dinner every night this week, you should dinner once in a while. Likely means you have a strong degree of certainty Will you cook dinner tonight. Reply: I love cooking dinner for you, babe, so most likely I will do it tonight as well. Probably means that you even even more certainty than just likely. Will you cook dinner tonight? Reply: Probably, have you ever seen me not cook dinner? None of these words imply 100% certainty. So if you actually didn't cook dinner, you can say, I never said I would cook dinner. I said, ("I probable/likely, possibly will cook dinner because at the time that I made that statement, I thought it was feasible.")

Possibly is more informal. It is an adverb. You use it to describe an action that could take place, or an action that could be true. It implies that it is less likely to actually happen. Example sentences: "I possibly forgot my keys." "Her name is possibly Karen." Likely is more formal. It is an adverb. You use it to describe an action that could take place, or an action that could be true. It generally implies that is more probable to take place than possible. Example sentences: "It's likely she is late again." "I'm likely to drink coffee in the morning." Feasible is very formal. It is an adverb. You use it to describe an action that could take place, or an action that could be true. It is generally used to mean less likely. Examples: "It is feasible that I missed a turn." If you are fairly certain something will happen, use likely/probably. If you are less use, use feasible/possible.