Master B2 Phrases with 'On': Boost Your English Vocabulary — B2 English vocabulary lesson by Langcom

Master B2 Phrases with ‘On’: Boost Your English Vocabulary

Raúl Maguiña

Fundador de Langcom | Examinador de Cambridge y del SIELE

septiembre 21, 2026

B2📚 Vocabulario⏱️ 6 min de lectura📅 Actualizado en septiembre de 2026
Understanding fixed phrases with the preposition on is essential for B2 English learners to sound natural and precise. These phrases are common in everyday conversation and formal contexts, helping you express specific ideas clearly. For example, you might buy something on offer to save money, or do something on purpose, meaning intentionally. Knowing these expressions improves your vocabulary and comprehension, especially for exams like the B2 First. They often have meanings that are not obvious from the individual words, so learning them as complete units is key. Mastering these idiomatic uses of on will significantly enhance your fluency and accuracy, allowing you to communicate more effectively in a wide range of situations. Langcom helps you learn these vital phrases to boost your confidence.

Why Are Prepositional Phrases Important in English?

Prepositions like on are small words, but they are very powerful. They connect words and ideas in sentences.

Sometimes, a preposition combines with a noun or adjective to form a fixed phrase. These phrases have a special meaning that you must learn as a whole.

  • Learning these phrases helps you speak more naturally.
  • They are common in both spoken and written English.
  • Understanding them improves your listening and reading skills.

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What Does 'On Offer' Mean?

When something is on offer, it means it is available at a reduced price. Shops use this to attract customers.

  • It is a temporary discount.
  • You can save money when items are on offer.

When Do We Use 'On Purpose'?

If you do something on purpose, you do it intentionally. It means you planned to do it, and it was not an accident.

  • It often implies a negative action, but not always.
  • It answers the question 'Why did you do that?'

Understanding 'On Duty' and 'On Leave'

The phrase on duty describes someone who is working at a specific time. They are performing their job responsibilities.

  • This phrase is often used for professions like police officers, nurses, or security guards.
  • The opposite is off duty (not working) or on leave (taking time off work, like a holiday).

How to Use 'On Average'?

Utilizamos on average to talk about a typical or usual amount, rate, or number. It means 'typically' or 'usually'.

  • You calculate it by adding several amounts and dividing by the number of amounts.
  • It helps to describe general trends or habits.

What is 'On Condition That'?

This phrase introduces a condition that must be met for something else to happen. It means 'only if' or 'provided that'.

  • It creates a dependent relationship between two actions or events.
  • The second part of the sentence will only happen if the first condition is true.

Explaining 'On Behalf Of'

When you do something on behalf of someone, you do it as their representative or for their benefit. You are acting for them.

  • It is used in formal situations, like accepting an award for someone else.
  • It can also mean 'in the interest of' or 'for the good of'.

Using 'On Balance' for Decisions

The phrase on balance means 'after considering all the facts' or 'when everything is taken into account'. You use it to give an overall opinion or conclusion.

  • It suggests you have weighed the pros and cons.
  • It helps to express a final judgment or summary.
Summary of Phrases with 'On'
Phrase Significado
On offer Available at a reduced price; a discount
On purpose Intentionally; not by accident
On duty Working; performing job responsibilities
On average Typically; usually; calculated mean
On condition that Only if; provided that; with the requirement that
On behalf of As a representative of; for the benefit of
On balance After considering everything; overall

Ejemplos

  • The new smartphones are currently on offer at a fantastic price.
  • I didn't mean to spill the coffee; it wasn't on purpose.
  • The doctor is on duty for the next eight hours.
  • On average, I read two books a month.
  • You can borrow my car on condition that you fill it with petrol.
  • She accepted the award on behalf of her entire team.
  • On balance, I think moving to a new city was the right decision.

Práctica

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Errores habituales de los hispanohablantes

Spanish speakers sometimes make mistakes with these phrases because they try to translate directly or use a different preposition.

  • Using 'in' instead of 'on': For example, saying in offer en lugar de on offer. Remember that on is fixed in these expressions.
  • Forgetting 'that' in 'on condition that': It's common to say on condition you help. The full phrase is on condition that you help.
  • Confusing 'on purpose' with 'by accident': These are opposites. On purpose means intentionally, while by accident means unintentionally.
  • Direct translation of 'on behalf of': While 'en nombre de' is a good translation, ensure you use on behalf of as a complete unit.

Always learn these phrases as complete units, not individual words, to avoid errors.

Preguntas más frecuentes

Are these phrases common in everyday English?

Yes, all the phrases taught here – on offer, on purpose, on duty, on average, on condition that, on behalf of, y on balance – are very common in everyday conversations and written English at the B2 level.

How can I remember these phrases?

The best way to remember them is to use them! Try to create your own example sentences for each phrase. Listen for them in movies, TV shows, and podcasts. You can also keep a vocabulary notebook and review them regularly. Practice makes perfect!

Will these phrases appear in the B2 First (FCE) exam?

Yes, vocabulary phrases like these are very likely to appear in the B2 First (FCE) exam, especially in the Reading and Use of English paper. You might find them in gap-fill exercises, multiple-choice questions, or even need to use them in the Writing paper to express yourself clearly and naturally.

Is 'on' always used with these words?

For the specific phrases we covered, yes, on is a fixed part of the expression. Changing the preposition would change the meaning or make the phrase incorrect. For example, you cannot say in offer o for purpose.

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Sobre el autor: Raúl Maguiña

Raúl Maguiña es el director de la Asociación Educativa Langcom, un centro autorizado de preparación para el examen Cambridge English en tu país. Con más de una década de experiencia en la enseñanza de idiomas y la certificación internacional, ha ayudado a miles de estudiantes, profesores e instituciones educativas de 25 países a conseguir las certificaciones de inglés de Cambridge, IELTS, TOEFL y Michigan.

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