Definition
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'.
Examples
- The team designed a series of experiments to test their hypothesis.
- Her hypothesis was that sleep deprivation impairs short-term memory.
- When the data contradicted the original hypothesis, the researchers revised it.
Synonyms
theory · premise · supposition · conjecture · proposition
In TOEFL & 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.