In the active voice, the subject of the sentence performs the action upon an object.

Sentences which use the active voice are usually more straightforward to understand as they are clear and direct.

For example:

The winner of the race lifted the trophy.

The doctor examined the patient.

Active voice affecting the object

A sentence written in the active voice emphasises the doer, or subject, of an action, who in turn affects an object.

For example:

Scientists have finally achieved efficient quantum-encrypted message transmission.

Here, the subject of the sentence (scientists) performed an action (achieved) that impacted an object (message transmission).

Active sentences put the focus on the ‘doer’ of the action, so use them when it's important who/what did something.

They're often used to focus on participants and experimental results.

Sentences in the active voice are generally clearer and more concise than those in the passive voice, which are typically longer and wordier.

Using the active voice in a sentence often means fewer words are used than in the passive voice.

For example:

Passive voice: The books were collected by the teacher. (7 words)

Active voice: The teacher collected the books. (5 words)

Ambiguity in the passive voice

Passive sentences can cause confusion because they can be vague about who is responsible for the action.

For example:

Who scored the goal? Doesn’t the writer know?

Reasons for using the active voice in your writing include:

Clarity and directness

The active voiceproduces unambiguous sentences. This makes it easier for the reader to understand who is performing the action.

Conciseness

Active sentences usually require fewer words than passive sentences. This makes sentences more succinct and to the point.

Engagement

The Active voice creates a more dynamic and engaging narrative.

Authority and responsibility

The Active voice assigns clear responsibility for actions. This can be important when writing technical or scientific reports, where accountability is crucial.

Comprehension

Active voice makes your writing easier to follow and understand.

A sentence written in the passive voice focuses on the object or action (verb) being performed by the subject.

The subject is often implied and needn’t be mentioned.

The passive voice can be useful for making writing sound more formal and objective by focusing on the result of an action rather than the person doing the action.

For example:

The data was collected by the researcher.

The data was collected.

Notice how, in that last example, the agent or doer of the action (verb) is not specified, focusing solely on the action (verb) and the object. Passive voice doesn't need a subject — it can be omitted (with all the ambiguity that might cause). Compare the above passive formulation with the active formulation of the same sentence, below, which can't work without the subject being there:

The researcher collected the data.

While the active voice is often encouraged for its clarity and directness, the passive voice holds a significant place in academic writing for several reasons:

To avoid using the first-person (I, we, you) - this maintains a formal tone:

• Active: I will argue that…
• Passive: It will be argued that…

To show interest in the person or object that experiences an action rather than the person or object that performs the action. 

• Passive: The castle was built in 1066. [we are interested in the castle rather than in who built it]

If we do not know who performed the action. 

• Active: The archaeologists found ancient artefacts in the cave.
• Passive: Ancient artefacts were found in the cave.

To create an authoritative or factual tone and objectivity:

• Active: The government enforces strict environmental regulations.
• Passive: Strict environmental regulations are enforced by the government.

Here's some tips to guide your choice between active and passive voice: 

Active voice

• Ideal for introductions, results, and discussion sections to present complex concepts clearly and directly.
• Enhances clarity and engagement by making sentences more dynamic.
• Preferred in non-scientific writing for most sentences to avoid confusion and maintain interest.
   

Passive voice

• Best suited for the methods section, where the focus is on the process rather than the researcher, emphasising the research actions over the doers.
• Offers an impersonal tone traditionally favoured in scientific writing and academic journals for its illusion of objectivity.
• Useful when the doer is unknown or irrelevant, or when aiming to highlight the recipient of an action.

Choosing the right voice 

When deciding between the active and passive voice, consider each sentence’s purpose and the overall tone of your work...

• Consider your discipline’s conventions and the clarity of your message.
• Review your writing for the balance of active and passive voice to ensure both are appropriately used. This balance can vary depending on the field, the purpose of the text, and specific sections within your work.