Good question. Here are some examples: I speak English. I am talking to you. I am speaking to you. I am telling you something. I am saying something to you. I will tell you something. I will tell you. I will say something to you. I will say something. There is more to the answer I would imagine, but: Speak is the only one of these used used directly with a language. You could also use say 'I can talk in English', but speak is the more common word, and doesn't require 'in'. Now the tricky part: talking and speaking are things you do to objects (generally people I guess, but whatever floats your boat*) Telling and Saying both involve passing information about something. Bizarrely, with tell it is necessary to say who you inform. With say, it is necessary to say what you are talking about. At least, that's what those examples indicate. I'd never really thought about it. And there's a bunch of idiomatic expressions that are exceptions to this anyway, things like: > I will say to you (kind of old fashioned) > I speak of something > I have heard talk of this And then, tell is used in the context of looking at an object and inferring something: I could tell by the way he walked, that he was in trouble. (Here, tell is a little like see) And also remember that say is used to informally introduce an idea: > Say, where did you buy that delicious cake. Or as an interjection to express astonishment or disbelief > "I have decided that I want to live at the south pole." My friend declared. > "Say what? That's crazy!" I replied, surprised. *Whatever floats your boat is an idiom suggesting you can do whatever makes you happy.

It's best to divide these 4 words into two pairs speak/talk and say/tell Speak/talk: Another member asked about this earlier today. Take a look here: http://www.italki.com/question/250988 Say/tell: 'Say' refers to the words that you say: eg say 'hello', say 'I'm sorry', say goodnight, say 'Can I help you?' You couldn't use 'tell' with these phrases above. 'Tell' refers to the information that you give: eg Tell me about your family I told the police what I had seen Don't tell anyone our secret There are also a number of set phrases with 'tell', such as 'tell a story' and 'tell the truth'. The other key difference between say and tell is that tell needs a direct object (me, you, us, your friends, the teacher) ie you need to say who you are telling. 'Say' doesn't need a direct object, but if you use a direct object, you must put 'to' before it. eg What did he say? or What did he say to you? He said he was sorry What did he tell you? He told me that his car had broken down.

You are getting "mixed" answers, and I am sure that there are good reasons why your respondents are answering as they do. I will offer my answer also. The critical term you used is the word "crucial". There is one "crucial" context as I see it. Say, Talk, Speak and Tell, are in general contexts, synonymous. I can say to you; "You sure are smart". I can Speak to you and say; "You sure are smart". I can tell you that "You sure are smart". I can talk to you about the things you do that show me that "You sure are smart". ============================= Those are all general expressions. Now, here is the exception with TELL. TELL can be used in an imperative context, and a very aggressive context, in a way the other words are usually not used. If I TELL someone something, it can be a mild exchange of information, but it can also be used rude in a way, because to TELL someone something is also an expression of authority, of dominance over another person. For example, if a person is very offended, they might respond this way: "Don't you ever tell me anything!" or Tell might be used this way, as an introduction to other aggressive or hostile remarks: "Let me tell you something!........(and so on and so forth)

The differences are very crucial - although they refer to the same concept, you cannot possibly replace one with another.

i think, that, thoose are similar, but depend the phrase you have to choose one of them!