I agree with Lee, Speak and Talk are very similar, but sometimes they're used differently. You use SPEAK when: • you speak a language • you ask to speak to someone on the telephone • you speak to a big group of people BUT, you use TALK when: • you talk about a subject • you talk when you have a conversation with someone.

This is one of those odd pairs of words that are very similar but not exactly the same. I speak to you and I talk to you, and there is no big difference in saying either. However there is a difference in sentences like "I speak English", it is not good to say "I talk English" purely because it is not common, although it makes perfect sense! Talk and speech are also nouns sometimes so "I give a talk to the students every day" and "I give a speech to the students every day" mean standing in front of students and conducting a monologue. Perhaps "talk" is less formal than "speech" and "talking" is less formal than "speaking" but the difference is very small.