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Preposition after adjective

Undecided about or undecided on?

Both undecided about and undecided on are standard. About is more common for general topics, while on often appears with decisions, choices, or plans.

Quick answer

How do about and on differ after undecided?

Use undecided about for a topic or situation and undecided on for a decision, option, or plan. In many contexts, both are possible.

I'm still undecided about the trip.
The committee is undecided on the final proposal.
She remains undecided about whether to apply.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
undecided about + topic

Talking about uncertainty in general

Use undecided about for subjects, situations, or future actions.

He is undecided about moving abroad.
We are still undecided about the schedule.
2
undecided on + choice

Referring to a specific decision

Use undecided on for options, selections, or formal decisions.

They are undecided on a name for the product.
The board remains undecided on the proposal.
3
undecided whether to + verb

Using a clause after undecided

Whether to can follow undecided without a preposition.

She is undecided whether to accept the offer.
I remain undecided whether to continue the course.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
undecided about
I'm undecided about the move.
General uncertainty about a topic or action.
undecided on
They are undecided on the budget.
Uncertainty regarding a choice or decision.
decided on
We decided on a new design.
A final choice has been made.
decided about
She has decided about her future plans.
Less focused on a specific selection than decided on.

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using the wrong preposition with choices

On is often more natural for selecting between options.

✕ The team is undecided about a winner. ✓ The team is undecided on a winner.

Adding a preposition before whether

Do not use about or on before whether to.

✕ She is undecided about whether to leave. ✓ She is undecided whether to leave.

Using undecided without context

Add information about the topic or decision when needed.

✕ We are undecided. ✓ We are undecided about the timing.

Quick practice

Choose the expression that matches the intended meaning.

1. I'm still ___ the new job offer.
2. The judges are ___ the final winner.
3. She is undecided ___ accept the invitation.

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Frequently asked questions

Are undecided about and undecided on both correct?

Yes. Both are standard, though they are used in slightly different contexts.

Which is more common for decisions?

Undecided on is especially common for choices, plans, and formal decisions.

Can I say undecided whether to?

Yes. This is a very common structure when talking about actions.

ubiquitous in, on, across, throughout or for? "ugly in", "ugly for" or "ugly of"? ultimate in, of, for, on or as? "unacceptable to", "unacceptable in" or "unacceptable for"? unaccounted for unaccustomed to or in? unacquainted with unaffected by, in, for or with? "unaffordable for" or "unaffordable to"? unanimous in, on, about, regarding or for? "unattractive to" or "unattractive for"? "unavailable for" or "unavailable to"?

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