Definitions
01scientific explanation
B2 · Upper Intermediate Countable noun Science Academic
n. a well-tested explanation that uses facts to show how a part of the natural world works.
n. a coherent set of propositions used as principles of explanation for a class of phenomena, typically confirmed through observation or experiment.
“In school, we studied the theory of evolution and how species change over time.”
“The general theory of relativity fundamentally altered our understanding of space, time, and gravity within the physical sciences.”
Usage
Often used with 'of' followed by the subject of study.
Synonyms
02principles vs practice
B2 · Upper Intermediate Uncountable noun Academic
n. the rules and ideas of a subject, rather than the actual doing of it.
n. the body of rules, ideas, and principles of a particular subject or skill as distinguished from its practical application.
“The course covers both music theory and how to play the piano.”
“While the candidate understood the theory of management, he struggled with the practical realities of leading a large team.”
Synonyms
Antonyms
03an idea or guess
B1 · Intermediate Countable noun Informal
n. an idea that someone has to explain something, even if it is not proven yet.
n. a hypothesis, conjecture, or individual opinion offered as an explanation for an event.
“I have a theory that the cat only meows when she wants treats.”
“Detectives are working on a theory that the two robberies were committed by the same group of people.”
Teaching tip
In casual conversation, 'theory' is often used where a scientist would prefer 'hypothesis' or 'guess'.
Synonyms
04mathematical logic
C1 · Advanced Countable noun Mathematics Technical · Academic
n. a set of rules and statements that are logically connected to each other.
n. a set of axioms and all the statements that can be logically derived from them within a formal system.
“The professor explained how set theory forms the basis of modern mathematics.”
“In model theory, we investigate the relationship between formal languages and their interpretations in various mathematical structures.”
Synonyms
Collocations
Common phrases and expressions where native English speakers use the word “theory” in context.
Verb
01. apply theory
“Students are encouraged to apply theory to real-world situations in their final projects.”
verb + noun
02. build theory
“Researchers collect data to build a theory about how children learn languages.”
verb + noun
03. construct theory
“It took years for the scientist to construct a theory that explained the phenomenon.”
verb + noun
04. develop theory
“The professor helped the students develop a theory for their sociology paper.”
verb + noun
05. formulate theory
“The detective began to formulate a theory about how the thief entered the building.”
verb + noun
Adjective
06. alternative theory
“If this idea is wrong, we need to consider an alternative theory.”
adj + noun
07. critical theory
“The course introduces students to critical theory in modern literature.”
adj + noun
08. current theory
“Current theory suggests that the universe is still expanding.”
adj + noun
09. economic theory
“Basic economic theory explains how supply and demand affect prices.”
adj + noun
10. general theory
“Einstein is famous for his general theory of relativity.”
adj + noun
11. modern theory
“Modern theory focuses more on the psychological aspects of consumer behavior.”
adj + noun
Noun
12. learning theory
“Teachers study learning theory to understand how to help their students succeed.”
noun + noun
Etymology
From Middle French théorie, from Late Latin theōria, from Ancient Greek θεωρία (theōría, “contemplation, divine perspective, speculation, a looking at, a seeking”), from θεωρέω (theōréō, “I look at, view, see, consider, examine”), from θεωρός (theōrós, “spectator”), from θέα (théa, “view, perspective, sight”) + ὁράω (horáō, “I see, look”) [i. e. θέαν ὁράω (théan horáō, “see, look at a view; survey + genitive”)].
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Word family
NOUN
ADJECTIVE
Related words
Domains
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B1 PreliminaryIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.4.0–5.0TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 3.0–3.544–71TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.550–784
- Frequency
- Very common
- Level
- B1 · IntermediateOxford
- Updated
- アルファベット
- 読み方の一覧 →
QR code
englishreference.com/q/theory
「カタカナ語」 data: JMdict (EDRDG), CC BY-SA 4.0