In English, sentences generally consist of three main parts:

1. Subject: The noun or pronoun that performs the action (e.g., he, she, they).
2. Verb: The word that gives the core meaning of the action (e.g., eat, write, see).
3. Object: The noun or pronoun on which the action is performed.

Example:
He is eating an apple.
In this sentence:

• He is the subject because he is performing the action.
• Apple is the object because the action is being performed on it.
• Eating is the verb, which gives the core meaning of the action, such as chewing and swallowing.

The action of a subject in relation to an object can be expressed in two ways, known as:

1. Active Voice
2. Passive Voice

Although the structure of a sentence changes when expressed in active or passive voice, its meaning remains the same. However, it changes the style of expression as follows:

• Active Voice: The subject acts upon the object.
• Passive Voice: The object is acted upon by the subject.

• Active Voice: Emphasizes the subject performing the action. It is direct, clear, and the most natural form of expression in everyday speech and writing.
• Passive Voice: Emphasizes the object receiving the action. It is used when the doer is unknown, unimportant, or deliberately omitted because more emphasis is placed on the object, making it common in scientific writing, formal reports, and objective statements.

Example:

• Active: The researcher conducted the experiment. → Focus on the researcher.
• Passive: The experiment was conducted. → Focus on the experiment.

The structure of sentence in active and passive voice can be expressed as follows:

Active voice: Subject + Verb + Object.
Passive voice: Object + Verb + Subject.

Remember, the structure of the sentence changes in active and passive voices, but the meaning the sentence remains the same whether expressed as active voice or passive voice. 

 Rule 1. Reversing Subject and Object: In passive voice, the subject and object are interchanged. The subject moves to the object’s position, and the object moves to the subject’s position.

 Rule 2. Changing the Verb Form:The main verb in passive voice is always in the past participle form (3rd form). Regardless of the form used in active voice, the verb must be converted to its 3rd form in passive voice.

 Rule 3. Use of ‘by’ :The word “by” is placed before the subject in passive sentences.

 Rule 4. Change in Helping Verb or Tense:In passive voice, the helping verb changes according to the tense of the sentence. Since each tense uses a specific helping verb (e.g., is, are, was, were, has, had, will), the rules for forming passive constructions vary accordingly. Detailed explanation for each tense is provided on this website.

 Rule 5. Expressing Subject (pronoun) as object (pronoun): As the subject shifts to the place of the object in passive, the subject pronoun (e.g. he, she, I, they, we) is expressed as object pronoun (e.g., him, her, me, them, us).

When converting pronouns from subject to object in passive voice, the following changes occur:

• he → him
• she → her
• I → me
• they → them
• we → us

The pronoun you remains the same.

 Rule 6. Omission of the Subject: In some cases, the subject may be omitted in passive voice when it is obvious or unnecessary to mention.

Note. Rules 1–3 and 5–6 apply to all sentences. Rule 4 is about the helping verbs and it varies depending on tense. Detailed explanations of tense-specific rules for it can be studied by clicking here.

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