SPEAK AND TALK
There is not very much difference between speak and talk.
In certain situations one or the other is preferred (though they are usually both possible).
Talk is the more usual word to refer to conversational exchanges and informal communication.
- When she walked into the room everybody stopped talking.
- Could I talk to you about the football match for a few minutes?
Speak is often used for one-way communication and for exchanges in more serious or formal situations.
- I have to speak to my boss.
- They had a terrible fight last week, and now they're not speaking to one another.
- After she had finished reading the letter, nobody spoke.
Talk is often used for the act of giving an informal lecture (a talk); speak is preferred for more formal lectures, sermons etc.
Speak is the usual word to refer to knowledge and use of languages, and to the physical ability to speak.
One usually asks to speak to somebody on the phone (US also speak with).
- Hello. Could I speak to Karen, please?
Talk is used before sense, nonsense and other words with similar meanings.
- You're talking complete nonsense, as usual. (NOT You're speaking complete nonsense ... )