Both speak and talk have the same meaning: to communicate ideas and thoughts by words, to utter words or articulate sounds.
They can be used interchangeably. However, there are some differences:
Speak is preferred on more official occasions and is usually used when one person addresses a group.
Talk is less formal and in most cases suggests conversation between two or more persons.
Both these verbs are usually intransitive (they don’t have a direct object after them). They are generally followed by a preposition (to/with, about, for) or by some adverbial modifier (much, less, in a quiet voice, a long time, etc.)
Talk is used more frequently than speak. Preposition to is more frequent than with.
Also, compare the nouns speaker and talker:
Remember the following phrases and proverbs with talk:
talk sense, nonsense, business, politics, baseball, etc.
talk bad, dirty, trash
talk shop = discuss work related issues
talk something over/through
talk somebody into something/doing something
talk somebody out of something/doing something
talk nineteen to the dozen
talk oneself hoarse
talk through one’s hat
talk big = show off, boast
talk one’s head off = to talk nonsense, brag, show off
talk turkey = talk about business, seriously
talk down = speak in a condescending manner, as if to a child
talk out = discuss until everything is agreed on, settled
talk like a Dutch uncle
TTYL = talk to you later (internet chat)
All talk and no trousers = synonym – all talk and no action
Now you are talking! (informal)
Great talkers are little doers.
Talk of the devil and he is sure to appear.
Remember the following phrases and proverbs with speak:
speak a language (speak English, speak Chinese, etc.)
so to speak = one can say, as it were
speak up = speak louder
frankly, generally, strictly, roughly speaking
speak the truth
speak fluently, easy
speak volumes = speak a lot
speak ill/evil of somebody
speak the word – express one’s wish
speak for oneself – to speak about one’s own opinion/feelings
speak one’s mind
speak to the subject – speak on the topic
the facts speak for themselves = the fact speaks for itself
this speaks him generous
nothing to speak of
the tongue speaks
speak against time
speak with a forked tongue = speak dishonestly, lie, make false promises
be on speaking terms with somebody
speak with plum in the mouth - showing that someone is from a very high social group.
Sasha is speaking. (on the phone)
Actions speak louder than words
When guns speak it is too late to argue.
A liar isn’t believed when he speaks the truth.
A truer word was never spoken.
A word spoken is past recalling.
Many speak much who cannot speak well.