verb
1
BAD : We hadn't seen each other for a year and so we spent the whole night speaking.
GOOD : We hadn't seen each other for a year and so we spent the whole night talking.
DUBIOUS : We spoke about where we would go for our next holiday.
GOOD : We talked about where we would go for our next holiday.
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When just one person does all or most of the talking, either speak or talk may be used: 'He spoke/talked about his years in the army.'
When two or more people have a conversation, the usual word is talk (NOT speak ): 'We must have been talking for hours.' 'If someone brings me a problem, we just sit down and talk about it.'
2
BAD : Neither of my parents speaks in English.
GOOD : Neither of my parents speaks English.
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speak in (English) = use (English) on a particular occasion: 'My grandparents won't understand a thing if the priest speaks in French.'
speak (English) = know (English) and use it habitually: 'Do you speak German?' 'We'll have to find someone who speaks English.'
3
BAD : We were shown how to speak with customers and handle complaints.
GOOD : We were shown how to speak to customers and handle complaints.
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In British English the usual phrase is speak to someone: 'If you need any more information, you should speak to Mrs Hall.'
Note that in American English both speak to and speak with are used.