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Idioms are fun phrases where the words together mean something totally different from what they say one by one. People use them to make talking and writing more colorful and exciting. In this lesson, you will learn fifty handy expressions related to things that can never happen, impossible tasks, and unreal dreams.
In this lesson, we’ll look at idioms that mean out of reach, unattainable, or completely unfeasible. Let’s get started and explore some of these helpful expressions.
Idioms for Something Impossible
1. When pigs fly
Definition: Something that will never, ever happen because it is completely impossible.
Used in a Sentence: He said he would clean his room without being asked when pigs fly. / Expecting the playful kitten to stop chasing yarn is like waiting for when pigs fly.
Similar Expressions: Never / Absolutely impossible
2. Once in a blue moon
Definition: An event that happens so rarely that it is almost impossible to witness.
Used in a Sentence: Seeing snow fall in the middle of summer happens once in a blue moon. / He only eats spicy peppers once in a blue moon because they are too hot.
Similar Expressions: Very rarely / Hardly ever
3. Hell freezes over
Definition: A humorous way to say something will happen at an impossible, infinite point in time.
Used in a Sentence: He joked that he would wear a winter parka when hell freezes over. / She promised to stop reading adventure books when hell freezes over.
Similar Expressions: Never gonna happen / Eternity away
4. Catch the wind
Definition: Trying to grab or control something that is completely intangible and impossible to hold.
Used in a Sentence: Trying to stop the fast-moving rumors was like trying to catch the wind. / He felt like he was trying to catch the wind when he chased floating bubbles.
Similar Expressions: Impossible mission / Futile effort
5. Reach for the moon
Definition: Setting a goal that is so grand and difficult it borders on the impossible.
Used in a Sentence: Building a working spaceship out of cardboard boxes felt like trying to reach for the moon. / The teacher told them to aim high, even if it felt like trying to reach for the moon.
Similar Expressions: Aim impossibly high / Grand dream
6. Pull yourself up by your bootstraps
Definition: An idiom describing a task that is physically impossible, since lifting boots while inside them defies gravity.
Used in a Sentence: Trying to lift the heavy box while standing inside it was like trying to pull yourself up by your bootstraps. / Expecting the broken toy to fix itself was like pulling yourself up by your bootstraps.
Similar Expressions: Impossible physical feat / Absurd task
7. Make a silk purse out of a sow’s ear
Definition: Trying to turn something low quality or worthless into something luxurious and fine.
Used in a Sentence: Trying to repair the ruined plastic toy into a brand-new masterpiece was like trying to make a silk purse out of a sow’s ear. / Fixing the old, rusted bicycle frame felt like making a silk purse out of a sow’s ear.
Similar Expressions: Impossible transformation / Hopeless upgrade
8. Paint the sky
Definition: Attempting an action that is completely beyond human ability and impossible to accomplish.
Used in a Sentence: Telling the young artist to fix the cloudy weather was like asking him to paint the sky. / Trying to change the past is as impossible as trying to paint the sky.
Similar Expressions: Unachievable task / Beyond power
9. Build castles in the air
Definition: Creating plans or dreams that have no foundation and are impossible to realize.
Used in a Sentence: Instead of doing his homework, he spent the afternoon building castles in the air about winning a medal. / Her wild plans to travel across space were just building castles in the air.
Similar Expressions: Daydreaming / Impossible fantasies
10. Bark up the wrong tree
Definition: Pursuing an impossible or completely mistaken line of action that yields no results.
Used in a Sentence: If you think you will find fresh fish in the dry desert sand, you are barking up the wrong tree. / Searching for the lost keys in the refrigerator meant he was barking up the wrong tree.
Similar Expressions: Wasting effort / Wrong approach
11. Wishful thinking
Definition: Believing that something impossible will happen simply because you want it to.
Used in a Sentence: Hoping the test would cancel itself automatically was just pure wishful thinking. / Thinking the broken toy would fix itself overnight was wishful thinking.
Similar Expressions: Empty hope / Daydream
12. Pie in the sky
Definition: An extravagant hope, plan, or promise that is completely unrealistic and impossible.
Used in a Sentence: His idea of opening a floating candy shop on a cloud was total pie in the sky. / Promises of getting a pony for every student sounded like pie in the sky.
Similar Expressions: Unrealistic dream / Impossible promise
13. A drop in the ocean
Definition: An amount so tiny compared to what is needed that it feels practically useless or impossible to make a dent.
Used in a Sentence: Giving one small bucket of water to fill the massive dry lake felt like a drop in the ocean. / Saving ten cents for a costly bicycle felt like a drop in the ocean.
Similar Expressions: Tiny fraction / Uselessly small
14. Shooting for the stars
Definition: Trying to achieve an extraordinary goal that is extremely difficult and close to impossible.
Used in a Sentence: Winning the national science fair on his first try was like shooting for the stars. / She knew becoming a champion skater meant shooting for the stars.
Similar Expressions: Aiming high / Massive ambition
15. Count your chickens before they hatch
Definition: Assuming an impossible or uncertain success before it has actually happened.
Used in a Sentence: Don’t buy a trophy before the race starts; you shouldn’t count your chickens before they hatch. / Planning how to spend prize money before winning is counting your chickens before they hatch.
Similar Expressions: Assuming success / Counting early
16. Lock the stable door after the horse has bolted
Definition: Trying to prevent a problem after it has already occurred and become impossible to reverse.
Used in a Sentence: Trying to apologize after the secret was already printed in the paper was like locking the stable door after the horse has bolted. / Checking the gate after the puppy escaped was locking the stable door after the horse has bolted.
Similar Expressions: Too late / Irreversible mistake
17. Cry for the moon
Definition: Desiring something that is completely unattainable and impossible to get.
Used in a Sentence: Asking for a pet dragon for your birthday is like crying for the moon. / Wishing to fly without wings is just crying for the moon.
Similar Expressions: Impossible desire / Wanting the unattainable
18. Chase rainbows
Definition: Pursuing illusory, unrealistic goals that can never be reached.
Used in a Sentence: Instead of studying practical math, he spent his time chasing rainbows of instant riches. / Trying to catch the end of a rainbow is chasing rainbows.
Similar Expressions: Chasing illusions / Unrealistic pursuit
19. Water off a duck’s back
Definition: Something that has zero effect, making it impossible to influence someone.
Used in a Sentence: Criticizing his funny hat was like water off a duck’s back because he loved it. / Trying to make the cheerful puppy worry was water off a duck’s back.
Similar Expressions: Unaffected / No impact
20. Lock horns
Definition: Engaging in an impossible stubborn struggle where neither side can win.
Used in a Sentence: The two stubborn brothers would lock horns over who got to sit in the front seat. / Arguing with the mule proved you were locking horns with a stubborn animal.
Similar Expressions: Stubborn clash / Deadlocked fight
21. Beat a dead horse
Definition: Wasting energy on an argument or task that is already finished and impossible to change.
Used in a Sentence: Complaining about yesterday’s rainstorm is just beating a dead horse. / Trying to fix the crushed paper cup is like beating a dead horse.
Similar Expressions: Pointless effort / Wasted energy
22. Carry water in a sieve
Definition: Attempting a task that is physically impossible because the tool leaks everything out.
Used in a Sentence: Trying to hold water in his cupped hands with holes in his gloves was like carrying water in a sieve. / Expecting the forgetful student to keep a secret was like carrying water in a sieve.
Similar expressions: Useless task / Bound to fail
23. Squeeze blood from a turnip
Definition: Trying to get money, resources, or results from a source that has absolutely nothing to give.
Used in a Sentence: Asking for extra allowance money from his broke piggy bank was like trying to squeeze blood from a turnip. / Expecting more answers from the empty book was like squeezing blood from a turnip.
Similar Expressions: Impossible extraction / Getting nothing
24. Needle in a haystack
Definition: A search so difficult that finding the object borders on the impossible.
Used in a Sentence: Locating the microscopic splinter in the rug was like finding a needle in a haystack. / Finding his lost contact lens on the lawn felt impossible, like a needle in a haystack.
Similar Expressions: Nearly impossible find / Hopeless search
25. Find water in the desert
Definition: Searching for a resource in a place where it is completely nonexistent and impossible to locate.
Used in a Sentence: Asking the closed grocery store for fresh milk at midnight was like trying to find water in the desert. / Looking for a snow shovel in July felt like trying to find water in the desert.
Similar Expressions: Nonexistent find / Impossible search
26. Part the Red Sea
Definition: A biblical idiom for performing an impossible miracle to clear a path.
Used in a Sentence: Getting the entire stadium crowd to leave in ten seconds would take parting the Red Sea. / Fixing the tangled computer network felt like parting the Red Sea.
Similar Expressions: Miraculous feat / Impossible rescue
27. Move mountains
Definition: Achieving a feat so massive and difficult that it requires supernatural effort.
Used in a Sentence: The dedicated volunteers worked together to move mountains and rebuild the playground. / Passing all four final exams with top scores felt like moving mountains.
Similar Expressions: Massive achievement / Incredible effort
28. Turn back the hands of time
Definition: Attempting to reverse time, which is completely impossible.
Used in a Sentence: He wished he could turn back the hands of time to avoid dropping his ice cream. / Regretting a mistake is easy, but you cannot turn back the hands of time.
Similar Expressions: Reverse time / Impossible rewind
29. Catch smoke with your bare hands
Definition: Trying to grasp something formless and impossible to catch.
Used in a Sentence: Trying to trap the drifting fog in a jar was like trying to catch smoke with your bare hands. / Pinning down his wild ideas was like trying to catch smoke with your bare hands.
Similar Expressions: Impossible grip / Uncatchable target
30. Teach a fish to climb a tree
Definition: Forcing someone to do a task that goes against their natural abilities, making it impossible.
Used in a Sentence: Asking the quiet, indoor cat to fetch a stick outside is like trying to teach a fish to climb a tree. / Forcing the tone-deaf singer to hit high opera notes felt like teaching a fish to climb a tree.
Similar Expressions: Unnatural task / Impossible training
31. Put the cart before the horse
Definition: Doing things in the wrong order, creating an impossible logistical knot.
Used in a Sentence: Buying paint before even building the birdhouse is putting the cart before the horse. / Trying to take the final exam before learning chapter one is putting the cart before the horse.
Similar Expressions: Wrong order / Backward logic
32. Make bricks without straw
Definition: Trying to complete an assignment without being given the necessary materials, making it impossible.
Used in a Sentence: Expecting the class to paint portraits without giving them any paint was making bricks without straw. / Writing an essay without any paper or pencils is making bricks without straw.
Similar Expressions: Impossible assignment / Lacking tools
33. A bridge too far
Definition: A plan or goal that goes too far beyond what is possible or safe to achieve.
Used in a Sentence: Trying to memorize all five hundred dictionary pages by tonight was a bridge too far. / Building a skyscraper out of popsicle sticks was a bridge too far.
Similar Expressions: Unrealistic goal / Overambitious plan
34. Mission impossible
Definition: A task or assignment that seems utterly impossible to successfully complete.
Used in a Sentence: Cleaning the massive muddy garage in ten minutes felt like a mission impossible. / Sneaking past the sleeping guard dog without making a sound was mission impossible.
Similar Expressions: Unachievable task / Impossible mission
35. Square peg in a round hole
Definition: Someone who does not fit into a group or situation, making harmony impossible.
Used in a Sentence: Putting the strict scientist into the whimsical art club felt like a square peg in a round hole. / Wearing heavy winter boots to swim in the pool made him feel like a square peg in a round hole.
Similar Expressions: Misfit / Incompatible fit
36. Oil and water
Definition: Two people or things that cannot mix, blend, or coexist peacefully.
Used in a Sentence: Cats and water are like oil and water; they never mix well. / Their opposing opinions on how to run the club meant they were like oil and water.
Similar Expressions: Incompatible / Unmixable
37. Reach for the stars
Definition: Striving for a goal so high it is practically impossible to attain.
Used in a Sentence: Dreaming of becoming the first astronaut from his town was reaching for the stars. / The young inventor knew creating a flying car was reaching for the stars.
Similar Expressions: Aiming sky-high / Impossible dream
38. Leap over the moon
Definition: A nursery rhyme expression representing something completely impossible.
Used in a Sentence: Expecting the cow sculpture to animate and leap over the moon is silly. / Wishing your troubles away instantly is like trying to leap over the moon.
Similar Expressions: Magical impossibility / Fairy-tale feat
39. Pull a rabbit out of a hat
Definition: Producing an unexpected, miraculous solution to an impossible problem.
Used in a Sentence: We had no money left for supplies, but the teacher managed to pull a rabbit out of a hat and find spare markers. / Solving the crisis at the last second was like pulling a rabbit out of a hat.
Similar Expressions: Miraculous fix / Sudden rescue
40. Whistling in the wind
Definition: Making appeals or taking actions that will have zero effect and are impossible to notice.
Used in a Sentence: Complaining about the heavy traffic to an empty road is just whistling in the wind. / Asking the stormy sky to stop raining is whistling in the wind.
Similar Expressions: Pointless appeal / Ignored voice
41. Tilt at windmills
Definition: Fighting imaginary enemies or engaging in a pointless, impossible battle.
Used in a Sentence: Arguing with the automated answering machine is like tilting at windmills. / He spent all afternoon tilting at windmills trying to fix a broken machine with no parts.
Similar Expressions: Fighting imaginary foes / Pointless battle
42. Ride two horses at once
Definition: Trying to pursue two contradictory, impossible paths simultaneously.
Used in a Sentence: Trying to play in two different soccer games scheduled at the exact same hour is trying to ride two horses at once. / Managing two opposite career goals at once is riding two horses at once.
Similar Expressions: Conflicting goals / Impossible multitasking
43. Have your cake and eat it too
Definition: Wanting two incompatible things at the same time, making it impossible.
Used in a Sentence: Wanting to eat all the cookies while still keeping them in the jar is trying to have your cake and eat it too. / Expecting to stay out late playing games while finishing homework early is having your cake and eat it too.
Similar Expressions: Contradictory desire / Impossible balance
44. Walk on water
Definition: A miraculous feat representing something impossible for ordinary humans to do.
Used in a Sentence: Expecting the rookie player to never make a single mistake is expecting him to walk on water. / Nobody is perfect; expecting someone to walk on water is unrealistic.
Similar Expressions: Miraculous expectation / Perfectionism
45. Straighten the curve of a pig’s tail
Definition: Attempting to alter something that is naturally crooked and impossible to fix.
Used in a Sentence: Trying to make the stubborn rulebreaker act quiet is like trying to straighten the curve of a pig’s tail. / Fixing the inherently flawed design was like straightening the curve of a pig’s tail.
Similar Expressions: Impossible fix / Unchangeable nature
46. Teach an old dog new tricks
Definition: Trying to change someone’s lifelong habits, which is famously difficult and nearly impossible.
Used in a Sentence: Grandfather refused to use the smartphone touchscreen, proving you cannot teach an old dog new tricks. / Trying to change how the veteran manager organized files was like trying to teach an old dog new tricks.
Similar Expressions: Resistant to change / Stubborn habits
47. Fireproof water
Definition: An imaginary substance that represents an impossible contradiction.
Used in a Sentence: Asking for a freezing hot blanket makes as much sense as asking for fireproof water. / His strange riddle described something as impossible as fireproof water.
Similar Expressions: Contradiction / Impossible concept
48. Push water uphill
Definition: Working against natural gravity to perform a task that is impossible.
Used in a Sentence: Trying to convince the stubborn crowd to change their minds felt like pushing water uphill. / Studying a subject you hate with zero guidance is like pushing water uphill.
Similar Expressions: Uphill struggle / Futile effort
49. Catch a falling star
Definition: A poetic way to describe capturing something that is unreachable and impossible to hold.
Used in a Sentence: Trying to grab the shooting star streaking across the night sky was like trying to catch a falling star. / Holding onto fleeting childhood memories is like trying to catch a falling star.
Similar Expressions: Unreachable goal / Impossible capture
50. Bring the dead back to life
Definition: A dramatic expression for something entirely impossible to achieve.
Used in a Sentence: Expecting the shattered ceramic mug to glue itself back together is like trying to bring the dead back to life. / Reversing the storm damage instantly is like trying to bring the dead back to life.
Similar Expressions: Total impossibility / Beyond repair
Exercise to Practice
- When pigs fly is an expression used to describe something that will happen tomorrow morning.
- Once in a blue moon describes an event that happens so rarely it is nearly impossible.
- Building castles in the air means creating practical, solid foundations for a real house.
- Barking up the wrong tree means pursuing a mistaken or impossible line of action.
- Squeezing blood from a turnip means getting plenty of easy resources from a rich source.
- Turning back the hands of time is a physical action that anyone can easily perform daily.
- Wishful thinking means believing something impossible will happen just because you want it to.
- A drop in the ocean represents a massive, overwhelming surplus of water.
- Putting the cart before the horse means doing things in the wrong, backward order.
- Teaching an old dog new tricks describes a very easy task with zero resistance.
- Catching the wind means trying to grasp something intangible and impossible to hold.
- Pie in the sky refers to a guaranteed, proven fact backed by science.
- Tilting at windmills means fighting imaginary enemies or engaging in a pointless battle.
- Pushing water uphill means working against natural forces on a futile task.
- Walking on water represents a realistic everyday task for ordinary people.
Answer Key
- False
- True
- False
- True
- False
- False
- True
- False
- True
- False
- True
- False
- True
- True
- False
Conclusion
Learning these idioms helps you understand common English expressions about impossible tasks, unreal dreams, and things that can never happen. Using them in your daily writing and conversations makes your speech much more colorful and fun.
Try picking one or two new expressions to use when talking with friends or writing stories this week. Practice makes perfect, and soon using these phrases will feel completely natural!
Frequently Asked Questions
What are some common idioms for something impossible?
Common expressions include when pigs fly, once in a blue moon, and pie in the sky. People use these phrases to describe unattainable dreams, absurd ideas, and things that will never happen.
Why do we use idioms in English?
Idioms make our language more expressive, colorful, and engaging than plain literal words. They help us share complex ideas quickly using fun mental pictures.
What does when pigs fly mean?
When pigs fly means something that will never happen because it is completely impossible. Since pigs do not have wings, the phrase uses a funny mental image to emphasize absolute impossibility.
How can I remember these idioms easily?
You can remember them best by making up fun sentences or drawing pictures for each phrase. Using them in daily conversations also helps lock them into your memory.
Are these expressions used in everyday conversation?
Yes, native speakers often use these idioms in books, movies, and regular chats. Knowing them helps you understand everyday English much better.
