rational
rational — adjective
1. involving decisions, beliefs, or actions that are based on facts and careful thi
involving decisions, beliefs, or actions that are based on facts and careful thinking rather than on feelings or personal wishes
Lisa made a rational choice to leave early and avoid the traffic.
collocation: rational choice
It is not always rational to let fear guide your decisions.
impersonal: it is rational to do something
The manager asked for a rational explanation of the budget problem.
Wei's argument was clear, rational, and supported by strong evidence.
There was no rational reason for closing the school during the storm.
- reasonable
more general; can apply to prices, amounts, and expectations, not just decisions
- logical
emphasises step-by-step reasoning and consistency rather than practical good sense
- sensible
practical and showing good judgment, with less emphasis on formal reasoning
- irrational
the direct opposite; based on emotion rather than reason
- emotional
driven by feelings, the opposite of detached logical thought
- unreasonable
not fair or sensible; often used for demands or expectations
文法句型
rational + noun
be rational to + infinitive
rational about + noun phrase
用法筆記
Evaluates specific choices, decisions, or arguments rather than a person's general thinking capacity — compare sense 2 (REASONING CAPACITY). Frequently used in the pattern 'it + be + rational + to-infinitive'.
常見錯誤
2. having the ability to think clearly, understand ideas, and make judgments based
having the ability to think clearly, understand ideas, and make judgments based on logic rather than feelings or instincts
Human beings are rational creatures who can plan for the future.
collocation: rational creatures
Theo was too upset to be rational about what had happened.
rational about + noun clause
Even young children show some rational thinking when solving simple puzzles.
A rational person considers the results of their actions before acting.
The court decided that the patient was not rational at the time of the accident.
- thinking
broader; describes any cognitive activity, not necessarily logical
- intellectual
emphasises the use of intellect and knowledge, often in academic contexts
- reasoning
emphasises the process of drawing conclusions from evidence
- irrational
lacking the ability to think logically; driven by instinct or emotion
- instinctive
based on natural impulse rather than reasoned thought
文法句型
rational + noun (being, creature, mind)
be rational about + noun phrase
not rational + adverbial
用法筆記
Describes beings (usually human) who possess the general capacity to think and reason. Compare sense 1 (LOGICAL THINKING), which evaluates individual actions rather than the person's overall faculty. In legal and medical contexts, 'not rational' can refer to a temporary state where judgment is impaired.
常見錯誤
3. describes any number you can write as a fraction made from two integers, like 1/
describes any number you can write as a fraction made from two integers, like 1/2, 3/4, or 7
Every whole number is rational because it can be written as a fraction.
predicative use with because-clause
Ishaan learned to add rational numbers like one half and three quarters.
collocation: rational numbers
The number 0.75 is rational because it equals three quarters.
Salma had to decide whether each number was rational or irrational.
- fractional
narrower; refers only to fractions, not whole numbers
- arithmetic
broader; describes any number used in basic calculations
- irrational
of a number that cannot be written as a fraction, such as π or √2
文法句型
rational + noun (number, expression)
用法筆記
Used only in mathematics. Never describes people or behavior. The opposite is irrational (a number that cannot be written as a simple fraction, such as π or √2).
常見錯誤
rational — noun
1. a number you can show as a simple fraction made from a pair of integers, such as
a number you can show as a simple fraction made from a pair of integers, such as 2, 1/3, or 0.75
All integers are rationals because each can be written over one.
plural form: rationals
The teacher asked the class to list five rationals between one and two.
use with quantity: five rationals
Soraya explained that a repeating decimal is also a rational.
Decimals that end are rationals, while some others go on forever.
- rational number
the full, formal term; 'rational' by itself is an abbreviation used in math contexts
- irrational
a number that cannot be written as a fraction of two whole numbers
文法句型
a rational
rational + plural -s
用法筆記
Used mostly in mathematics textbooks and classroom settings. The plural form is 'rationals'. When spoken, the word sounds the same as the adjective — /ˈræʃ.nəl/ — so context determines the part of speech.