Ministry of higher and secondary specialized education of the republic of uzbekistan

She can play violin.

Mary is from Chicago.

In this case the words ‘can‘ and ‘is from‘ are weak form. The weak form change the vowel to “ə” sound.

• 
  can in strong form: /kæn/
  
• 
  can in weak form: /kən/
  
• 
  from in strong form: /frɔm/
  
• 
  from in weak form: /frəm/
  

Below are some function words that you can remember:

• 
  auxiliar verbs am, are, be, been, can, could, do, does, has, had, shall, should, was, were, would,
  
• 
  prepositions at, for, from, of, to,
  
• 
  pronouns he, her, him, his, me, she, them, us, we, you,
  
• 
  conjunctions for, and, but, or, than, that,
  
• 
  particles to,
  
• 
  articles a, the, an,
  

The weak form is usually used in everyday English conversation, especially when speaking fast. But there are many situations you have to speak in strong form for the followings:
1. Stand at the end of sentence

• 
  What are you looking at (/æt/)?
  
• 
  Where are you from (/ frɔm/)?
  

2. In the contrast situations

• 
  The letter is from him, not to him. /frɔm/ /tu/
  
• 
  He likes her, but does she like him? /hə:/ /him/
  

3. Stress on opposite prepositions

• 
  I travel to and from London a lot. /tu/ /frɔm/
  

4. Stress on the purpose of the meaning.

• 
  You must get the unniversity certificate to have good job in the future. /mʌst/
  
• 
  You must choose us or them, you cannot have all. /mʌst/
  

The words that have two syllables or more will have the strong pronunciation and weak pronunciation. The vowel of the weak pronunciation will be chaned to /ə/ sound.