Understanding Active and Passive Voice Conversion

Converting sentences from active voice to passive voice involves changing the structure so that the object of the active sentence becomes the subject of the passive sentence. The verb form also changes, typically involving a form of 'be' and the past participle (V3) of the main verb. When dealing with modal verbs, the structure follows a specific pattern.

Analyzing the Given Active Sentence

The active voice sentence provided is: "She might have completed her research by that time."

Let's break down its components:

• Subject: She
• Modal Verb: might
• Auxiliary Verb: have
• Main Verb (V3): completed
• Object: her research
• Time Phrase: by that time

The structure is Subject + Modal + have + V3 + Object + Time Phrase.

Rule for Modal Perfect Passive Voice

When converting an active sentence with a modal verb followed by 'have' and the past participle (Modal Perfect Active) to passive voice, the general structure is:

Object + Modal Verb + have + been + V3 (past participle) + by + Subject (as agent) + other elements (like time phrase)

Applying the Rule to the Sentence

Using the rule described above, let's convert the sentence "She might have completed her research by that time" to passive voice:

• The object of the active sentence, "her research," becomes the subject of the passive sentence.
• The modal verb "might" is retained.
• "have been" is added after the modal verb.
• The past participle "completed" remains the same.
• The subject of the active sentence, "She," becomes the agent introduced by "by her".
• The time phrase "by that time" is included.

Following these steps, the passive voice sentence is: Her research might have been completed by her by that time.

Evaluating the Options

Let's examine each option based on the correct passive voice structure:

1. Her research might be completed by her by that time.
   This option uses "might be completed," which is the passive form for "might complete" (Modal + Base Verb). It does not match the original structure which includes "might have completed" (Modal + have + V3). Therefore, this is incorrect.
2. Her research might had been completed by her by that time.
   This option incorrectly uses "had been completed" after "might". The correct form after "might have" in passive voice is "might have been". The structure "might had been" is grammatically incorrect. Therefore, this is incorrect.
3. Her research might have been completed by her by that time.
   This option follows the correct passive structure: Object (Her research) + Modal (might) + have + been + V3 (completed) + by + Agent (her) + Time Phrase (by that time). This matches the expected passive form. Therefore, this is correct.
4. Her research might have completed by her by that time.
   This option uses "might have completed" which is the active voice structure. It lacks the necessary "been" for the passive voice construction with modal perfect verbs. Therefore, this is incorrect.

Conclusion on Passive Voice Conversion

Based on the analysis of the original active sentence structure (Modal + have + V3) and the rules for converting to passive voice (Modal + have + been + V3), the correct passive form is found in option 3.

Revision Table: Active vs. Passive Voice

Additional Information on Passive Voice Agents

In passive voice sentences, the original subject (the doer of the action), often called the agent, is typically introduced by the preposition "by". However, the agent is often omitted in passive sentences when:

• The agent is unknown.
• The agent is unimportant.
• The agent is obvious from the context.
• The focus is primarily on the action or the object receiving the action.

For example, "Her research might have been completed by that time." This sentence omits the agent "by her," and it is still a grammatically correct and often preferred passive construction when the focus is on the completion of the research, not who completed it.