These two words are often confused by learners of English, and I can see why: the meanings are similar. Sometimes, natives use speak and talk interchangeably (in a way that can be exchanged) and sometimes the meaning is different. I’ll give some examples and explain below.
Speak – to vocalise your thoughts and feelings, often not in a conversation.
Talk – to converse with other people.
Here’s a few examples:
“Please be quiet when I am speaking.”
You might have heard a teacher say this. They are addressing the class, not in a conversation.
“I was talking to your mother yesterday.”
The speaker and the person’s mother are having a conversation.
It’s important to remember this, because if you use these two words in this way, you won’t make a mistake!
When we only use ‘speak’ or ‘talk’
Like I said, you will hear natives using these words interchangeably, but there are situations where one word is correct and the other is incorrect.
“I can speak 3 languages”.
The person is referring to themselves, they are not having a conversation, so ‘speak’ is correct. Using ‘talk’ here is incorrect.
“They are talking in Italian”.
There is more than one person having a conversation, so ‘talk’ is correct.
“Elon Musk will speak at the end of the conference”.
If a person is addressing a group of people, it’s correct to use ‘speak’. Remember, this is not a conversation.
When they are used interchangeably
If either of these words are followed by ‘to’ or ‘with’, then you can use either:
“I’ll speak to you tomorrow/I’ll speak with you tomorrow.”
“I’ll talk to you tomorrow/I’ll talk with you tomorrow.”
There is no real difference between any of these sentences, so you can use any of them to express the same idea.
Speak is more formal than talk
In formal settings, like at work, it’s more natural to use ‘speak’, though you won’t get into trouble if you use ‘talk’!