Are there sentences that cannot be changed to active voice?

In one line

Some sentences cannot be changed to active voice because they have no clear doer (subject) or use special verbs.

The rule

Only sentences with a clear subject (doer), verb, and object can be changed from passive to active voice.

Formula: Active: Subject + Verb + Object | Passive: Object + form of 'to be' + Past Participle + (by + Subject)

Let's understand it simply

Imagine you are playing cricket. If you know who hit the ball, you can say, “Rahul hit the ball.” That’s active voice. But sometimes, you only know, “The ball was hit.” You don’t know who did it. In such cases, you cannot change the sentence to active voice because there is no doer.

When can you change to active voice?

Passive Sentence	Can you change?	Why
The cake was eaten by Riya.	Yes	Doer (Riya) is given.
The cake was eaten.	No	Doer is missing.
The meeting was held yesterday.	No	No doer, no object.
The letter was written by the teacher.	Yes	Doer (teacher) is given.

How it works

Look for the doer (subject) in the passive sentence.
If the doer is mentioned (like 'by the teacher'), you can change it to active voice.
If the doer is missing or unknown, you cannot change it to active voice.
Some passive sentences use verbs that do not take an object (intransitive verbs), so they cannot be made active.

How to check if a passive sentence can be made active

Find the doer (after 'by').
If doer is present, rewrite as: Doer + Verb + Object.
If doer is missing, you cannot change it.
Check if the verb needs an object (transitive).

The story behind it

English grammar rules were made to help people communicate clearly. The idea of active and passive voice comes from the need to show who is doing the action. But sometimes, we do not know or do not want to say who did it. That’s why some sentences are only possible in passive voice.

Where you see it in real life

News reports: “A wallet was stolen.” (Doer not known)
Notice boards: “The meeting has been postponed.” (Who postponed it? Not mentioned)
Instructions: “You are requested to keep silence.” (Who is requesting? Not clear)
Science experiments: “The solution was heated.” (Who heated it? Not given)

Why it matters

Helps you write clear sentences in essays and letters.
Useful for exams where you are asked to change voice.
Helps you understand when to use passive voice (when doer is unknown or unimportant).
Makes you careful about giving complete information.

Common mistakes

Thinking every passive sentence can be changed to active. (Not true if doer is missing)
Trying to make intransitive verbs active. (E.g., “He is gone” cannot be made active)
Forgetting to look for the word 'by' to find the doer.