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hypothesis

/haɪˈpɑːθəsɪs//haɪˈpɒθəsɪs/·noun
a proposed explanation used as a starting point for investigation
Fig. 1 — Before anything is thrown, a dashed arc is drawn through the air, curving from the launcher to a small marked spot on the ground — a flat claim about exactly where the ball will come down.
01Definition

A hypothesis is an educated guess with a job to do: a tentative explanation, based on limited evidence, that researchers then set out to test. It is not a wild guess — a good hypothesis is grounded in observation — but it is not yet knowledge either. It lives in the space between an idea and a confirmed theory, and the whole machinery of experiments exists to decide whether it survives. The plural is 'hypotheses'.

02In use
  • iThe team designed a series of experiments to test their hypothesis.
  • iiHer hypothesis was that sleep deprivation impairs short-term memory.
  • iiiWhen an anomaly in the data contradicted the hypothesis, the researchers revised it.
03Collocations
  • test a hypothesis
  • formulate a hypothesis
  • support the hypothesis
  • reject a hypothesis
  • a working hypothesis

Family hypothesize (verb) · hypothetical (adjective) · hypotheses (plural)

04Relations

=theory, premise, notion, conjecture, proposition

≠established fact, certainty

06TOEFL & IELTS

Arguably the single most important word in TOEFL science passages, which constantly narrate the cycle of proposing, testing, and rejecting hypotheses. Listening lectures use phrases like 'this supports/undermines the hypothesis' — recognize them as signposts for main-idea questions. Remember the irregular plural 'hypotheses' and the verb collocations: formulate, test, confirm, reject.

07Asked
What is the plural of hypothesis?
The plural of hypothesis is hypotheses — never 'hypothesises', a common error (that spelling exists only as a UK verb form). Like other Greek borrowings, the -is ending changes to -es: the same pattern as analysis → analyses, thesis → theses, and crisis → crises. Learn one and you have learned them all.
How do you pronounce hypotheses?
Hypotheses is pronounced hy-POTH-uh-seez: the final syllable is /siːz/, not /sɪs/. That final syllable is the only audible difference between singular and plural, so listeners rely on it entirely. In American English the second syllable is /pɑː/, in British English /pɒ/.
What is the difference between a hypothesis and a theory?
A hypothesis is a proposed explanation still waiting to be tested; a theory is an explanation that has already survived extensive testing. In science the two words mark stages, not strength of belief — a hypothesis that keeps passing experiments may become part of an established theory, never the other way round.
Is a hypothesis just an educated guess?
Only half. Like an educated guess, a hypothesis is built from what you already observe — but it must also be testable: precise enough that an experiment could prove it wrong. In the scene above, the dashed arc is drawn before the throw for exactly that reason — so reality can check the claim.
What is a null hypothesis?
A null hypothesis is the default assumption that there is no effect or no relationship — the claim an experiment tries to reject. Researchers phrase it negatively ('the drug makes no difference') so that any real effect has to prove itself against it. The term is everywhere in academic reading on statistics.
What is the verb form of hypothesis?
The verb is hypothesize (US) or hypothesise (UK): to propose something as a hypothesis. Note the spelling split between American -ize and British -ise — both are accepted in IELTS writing, but stay consistent within one essay.
What does 'working hypothesis' mean?
A working hypothesis is a provisional explanation a team adopts to keep moving — good enough to guide the next experiment, held loosely enough to drop when the data disagree. The phrase signals humility: 'this is what we assume for now', not 'this is what we believe'.