I know there is no strict rule on pronunciation of words in English but here my question is about the words which begin with 'con' and 'com', more than asking general rule.
When I look at the words begin with 'con' and 'com', I see mostly two patterns : One of them is schwa /ə/ sound and the other one is /o/ or /ɒ/ sound.But the second pronunciation can be pronounced slightly differently depending on dialect.
An example word for the first pronunciation is the word computer whose pronunciation is represented /kəmˈpjuː.tər/ in Cambridge Online Dictionaries.
An example for the second type of pronounciation for "co" could be the word contrast whose pronunciation is represented /ˈkɒn.trɑːst/ in Cambridge Online Dictionaries.
So my question is there any rule/pattern which can help us guess how to pronounce these words correctly?
I am not asking about the words like cool, come or coke. My question is about words like contract, combination, continue, combat.