Infeasible or Unfeasible: Which Word Is Correct?

“Infeasible” and “unfeasible” are both correct words, but “infeasible” is more common. Infeasible: Not possible or practical to do. Unfeasible: Also means not possible or practical, but it is less commonly used.

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Have you ever wondered if to write infeasible or unfeasible? Both words look correct, and both can describe something that cannot be done or achieved. But which one should you use in your writing?

The good news is that both infeasible and unfeasible are correct English words. They have the same basic meaning: not possible or not practical to do. However, infeasible is a common choice in formal, technical, business, and academic writing.

You may see unfeasible in general writing, too. It is not simply a spelling mistake. The best choice depends on your audience, writing style, and the context.

In this guide, you will learn the meaning of each word, how they differ in usage, and how to choose the right one for your sentence.

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Quick Answer: Infeasible vs. Unfeasible

Infeasible and unfeasible both mean that something is not possible or practical to do. Neither word is automatically incorrect.

• Infeasible: A common choice in technical, academic, business, and formal writing.
• Unfeasible: An accepted alternative with the same basic meaning.
• Not feasible: A simple and clear alternative that works well in everyday English.

For most formal reports, research papers, and professional documents, infeasible is a sensible default. If you prefer simpler language, not feasible is also a good choice.

Word	Meaning	Common use
Infeasible	Not possible or practical	Formal, technical, and professional writing
Unfeasible	Not possible or practical	General and formal writing
Not feasible	Not possible or practical	Everyday and professional writing

Remember: The difference is mainly about usage and preference, not a difference in meaning.

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What Does Infeasible Mean?

Infeasible is an adjective. It describes something that cannot be done, achieved, or put into practice under the conditions that exist.

A plan may be infeasible because it costs too much, takes too long, needs resources that are not available, or faces practical limits.

The word does not always mean that something is impossible forever. It may mean that the task cannot be completed with the current time, money, tools, or other resources.

For example:

• The project is infeasible because the budget is too small.
• Completing the work in one day is infeasible.
• The team found the original design infeasible.
• The company rejected an infeasible business plan.
• Building the road without enough funding would be infeasible.

In each sentence, infeasible describes a plan, task, or idea that cannot work under the stated conditions.

When Should You Use Infeasible?

Use infeasible when you want to explain that a plan or action cannot work in practice.

It is especially useful in writing about:

• Business plans and budgets
• Engineering projects
• Scientific research
• Computer science and mathematics
• Project deadlines
• Public policy and planning
• Academic studies

For example, a project manager may call a deadline infeasible if the team cannot finish all the required work in the available time.

An engineer may describe a design as infeasible if it cannot meet the required technical limits.

In these situations, the word helps explain that a plan has practical or technical problems.

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What Does Unfeasible Mean?

Unfeasible is also an adjective. It means not feasible, not practical, or not possible to achieve under the circumstances.

It has the same basic meaning as infeasible. The difference is not that one describes an impossible task while the other describes a difficult task. Both words can describe plans that cannot realistically be carried out.

For example:

• The plan became unfeasible after the costs increased.
• The team considered the deadline unfeasible.
• The proposal was unfeasible with the money available.
• It would be unfeasible to complete the repairs overnight.
• The original idea proved unfeasible in practice.

These sentences use unfeasible in the same way that they could use infeasible.

Is Unfeasible a Real Word?

Yes. Unfeasible is a recognized English word, not simply a typing error.

Cambridge Dictionary lists unfeasible and notes infeasible as an alternative. It defines the word as something that cannot be done or achieved. <Cite refs={“turn380842search9″,”turn380842search15″”turn380842search9″,”turn380842search15”}/>

You may find advice online that says unfeasible is always wrong. That advice is too strong. A word can be less common in a particular type of writing without being incorrect.

If your school, employer, publisher, or style guide asks you to use infeasible, follow that preference. Otherwise, you can use either word where it fits naturally.

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What Is the Difference Between Infeasible and Unfeasible?

The main difference is how writers choose to use the two forms. Their core meanings are the same.

Infeasible is a common choice in professional and technical writing. It often appears when writers assess plans, systems, designs, costs, or technical limits.

Unfeasible is another valid way to express the same idea. It may be used in general writing and can appear in professional contexts as well.

Compare these sentences:

• The project is infeasible because the budget cannot cover the costs.
• The project is unfeasible because the budget cannot cover the costs.

Both sentences communicate the same message. The spelling changes, but the meaning does not.

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Comparison Table

Feature	Infeasible	Unfeasible
Part of speech	Adjective	Adjective
Basic meaning	Not possible or practical	Not possible or practical
Correct English word?	Yes	Yes
Used in formal writing?	Yes	Yes
Used in technical writing?	Common	Also possible
Can describe a plan?	Yes	Yes
Can describe a deadline?	Yes	Yes
Simple alternative	Not feasible	Not feasible

You do not need to memorize a strict rule that assigns a different meaning to each word. There is no widely accepted rule that makes one word mean “technically impossible” and the other mean “merely inconvenient.”

Are the Words Interchangeable?

In most sentences, yes. You can replace infeasible with unfeasible without changing the main meaning.

However, the best word can depend on your audience and the type of document you are writing.

A technical report may use infeasible because that is the preferred term in the writer’s field. A general article may use unfeasible or the simpler phrase not feasible.

The important point is to avoid creating a difference in meaning where none is needed.

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Infeasible or Unfeasible in American and British English

This pair is not like color and colour, where the spellings are strongly linked to different regional conventions.

Both infeasible and unfeasible are used in English, including American and British English. The choice is better understood as a matter of usage and context than as a strict US-versus-UK spelling rule. Cambridge recognizes both forms in its dictionary entries.

For a broad international audience, infeasible is a practical choice in formal and technical writing. It is also useful when your document needs to follow a professional style.

You should not assume that every British writer prefers unfeasible or that every American writer rejects it. Such a rule would be too simple for actual English usage.

Which Word Is Better for Global Readers?

If your article is aimed at readers in the United States, the United Kingdom, Canada, Australia, or other English-speaking regions, either word can be understood.

For professional or technical content, choose infeasible unless your organization follows another established preference.

For a general audience, you can also write not feasible. This phrase is direct, familiar, and easy to understand.

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Why Are There Two Words?

Both words come from the base word feasible, which means possible or practical to do.

English uses prefixes to change the meaning of words. The prefixes in- and un- can both express a negative meaning in certain words.

• Feasible: possible or practical to do
• Infeasible: not feasible
• Unfeasible: not feasible

This is why both forms exist.

English does not always follow one simple rule for choosing a negative prefix. Some combinations become common through long use, while others remain less frequent. The fact that a word uses un- rather than in- does not automatically make it wrong.

What Does Feasible Mean?

Feasible is an adjective that describes something that can be done or achieved in a practical way.

For example:

• The plan is feasible with our current budget.
• The team believes the deadline is feasible.
• The design is feasible with the available materials.

The negative forms describe the opposite situation.

For example:

• The plan is infeasible with our current budget.
• The deadline is unfeasible for the team.
• The design is not feasible with the available materials.

Understanding feasible makes it easier to understand both infeasible and unfeasible.

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Infeasible vs. Impossible vs. Impractical

These words are related, but they do not always have exactly the same tone.

Infeasible means a plan or task cannot realistically be done under the current conditions.

Impossible usually makes a stronger statement. It suggests that something cannot happen or be done at all, though people sometimes use it informally to describe something extremely difficult.

Impractical means something is not sensible, useful, or convenient to carry out. An impractical idea may still be possible.

Compare the following sentences:

Word	Meaning	Example
Infeasible	Cannot realistically be achieved under the conditions	The project is infeasible without more funding.
Impossible	Cannot be done or cannot happen	It is impossible to be in two places at once.
Impractical	Not sensible or convenient to carry out	The design is impractical for a small room.
Unworkable	Cannot function successfully in practice	The proposed schedule is unworkable.
Unachievable	Cannot be reached or attained	The target is unachievable with the current resources.

These words may overlap, but you should choose the one that best matches your meaning.

For example, a plan that needs more money may be infeasible now but possible if funding increases. Calling it absolutely impossible could suggest something stronger than you intend.

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Common Mistakes With Infeasible and Unfeasible

Understanding the meaning of both words can help you avoid common writing mistakes.

Mistake 1: Saying Unfeasible Is Always Wrong

This is a common misunderstanding.

Incorrect claim: Unfeasible is never a correct English word.

Correct information: Both infeasible and unfeasible are recognized words with the same basic meaning.

Use the spelling that suits your context or follows your required style guide.

Mistake 2: Giving the Words Different Meanings

Some explanations suggest that infeasible means completely impossible, while unfeasible means only difficult or impractical.

There is no general rule that supports this distinction. Both words can describe something that is not possible or practical to achieve.

Do not rely on that difference when choosing a word.

Mistake 3: Assuming the Choice Depends Only on Country

It is too simple to say that American English always uses infeasible and British English always uses unfeasible.

Both forms appear across English-speaking regions. The type of writing and the writer’s preferred style can matter more than location.

Mistake 4: Using a Complicated Word When a Simple Phrase Works

Sometimes, the clearest choice is not feasible.

For example:

• Formal: The proposal is infeasible under current conditions.
• Simple: The proposal is not feasible under current conditions.

Both sentences are correct. The second may be easier for readers who prefer plain English.

Mistake 5: Changing Spelling Without a Reason

If you use infeasible throughout a report, avoid switching to unfeasible without a reason.

This does not mean the second word is wrong. Consistent wording simply makes the document easier to read.

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How to Choose the Right Word

Use these simple guidelines when you are unsure.

Choose infeasible when writing a technical report, research paper, engineering document, business plan, or formal assessment.

Choose unfeasible when you prefer that accepted form and it fits the tone of your writing.

Here are a few more examples:

• Business: The expansion plan is infeasible without additional funding.
• School: The teacher explained why the proposed schedule was infeasible.
• Engineering: The design was considered infeasible under the required safety limits.
• Everyday writing: It would be unfeasible to finish all the work tonight.
• Plain English: It is not feasible to finish all the work tonight.

All five sentences communicate a practical limit. The wording changes to suit the context.

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Fill in the Blanks

Complete each sentence with the correct word.

1. Both infeasible and unfeasible mean not possible or not __________ to do.
2. The word that is often used in technical writing is __________.
3. The base word __________ means possible or practical to do.
4. A simple alternative to infeasible is “not __________.”
5. The noun form of infeasible is __________.

Answer Key

1. Practical
2. Infeasible
3. Feasible
4. Feasible
5. Infeasibility

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Mini Quiz

1. Which statement is correct?

A. Only infeasible is a real word.
B. Both infeasible and unfeasible are correct.
C. Both words mean completely different things.

Answer: B. Both words are accepted and share the same basic meaning.

2. What does infeasible mean?

A. Easy to complete
B. Not possible or practical to do
C. Already finished

Answer: B. It describes something that cannot realistically be achieved under the conditions.

3. Which word is a sensible choice for a technical report?

A. Infeasible
B. Feasibilityless
C. Unpossible

Answer: A. Infeasible is commonly used in technical and professional writing.

4. What does feasible mean?

A. Possible or practical to do
B. Too expensive in every case
C. Not allowed by law

Answer: A. A feasible plan can be carried out in a practical way.

5. Which phrase is a clear alternative to both words?

A. Not feasible
B. Not feasibility
C. Unfeasibilityable

Answer: A. “Not feasible” is simple, clear, and grammatically correct.

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FAQs

Is infeasible or unfeasible correct?

Both are correct English words. They mean not possible or not practical to do. Infeasible is a common choice in technical and professional writing, while unfeasible is an accepted alternative.

Is unfeasible a misspelling of infeasible?

No. Unfeasible is not simply a misspelling. It is a recognized adjective with the same basic meaning as infeasible.

Which word is more common?

Infeasible is a common choice in formal, academic, business, and technical writing. Exact frequency can vary by time period, region, and type of text, so it is best not to claim that one word is preferred in every situation.

Can I use unfeasible in formal writing?

Yes, it is a valid word. However, if you are writing for a technical field, a university, or an employer with a style guide, follow that guide’s preferred term. Infeasible is a sensible default for many professional documents.

Is there a difference between infeasible and impossible?

They are similar, but impossible can sound stronger. Infeasible often refers to something that cannot realistically be achieved under current conditions. A plan may become feasible if those conditions change.

Is not feasible better than infeasible?

Neither phrase is always better. Not feasible is plain and easy to understand. Infeasible is concise and often suits formal or technical writing. Choose based on your audience.

What is the opposite of infeasible?

The opposite is feasible, which means possible or practical to do. Depending on the sentence, workable, achievable, or practical may also express the opposite idea.

What is the noun form of infeasible?

The noun is infeasibility. It refers to the state or condition of being infeasible.

For example: The report explained the infeasibility of the original plan.

Do infeasible and unfeasible have the same pronunciation?

They are usually pronounced differently at the beginning because they start with different prefixes. Infeasible begins with the sound “in,” while unfeasible begins with the sound “un.” Both share the ending “feasible.”

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Conclusion

When choosing between infeasible or unfeasible, remember that both words are correct. They share the same basic meaning: not possible or practical to do.

The main difference is usage preference. Infeasible is a sensible choice for technical, academic, and professional writing. Unfeasible is also accepted, and it is not automatically a spelling mistake.

If you want the simplest wording, use not feasible. It is clear, natural, and easy for most readers to understand.

The best rule is simple: choose the word that fits your audience, follow any style guide you need to use, and keep your wording consistent.

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