Active Voice : In the active voice, the object receives the action of the verb. Active voice is a voice that indicates a subject that has the semantic function of actor.
Example : He cut the tree.
Passive Voice : In the passive voice, the subject receives the action of the verb. Passive voice is a voice that indicates that the subject is the patient or recipient of the action denoted by the verb.
Example : The tree was cut by him.
From object to subject
Object position - subject position
Me - I
Us - We
You - You
Him - He
Her - She
Them - they
It - It
The verb will agree in number and person with the subject in the Passive voice. If the subject in the active sentence is unknown or unimportant or obvious (e.g. Somebody, Someone, People) , BY + OBJECT is omitted from the sentence in the Passive Voice.
We make butter from cow’s milk.(active)
Butter is made from cow’s milk.(passive)
The postman delivered twice a day.(active)
Letters are delivered twice a day.(passive)
Some one has stolen my purse.(active)
My purse has been stolen by someone.(passive)
If the verb in the active voice sentence has a modal in it, the verb is changed into its Passive voice in the following way :
Modal + be + the past participle form of the verb.