Prefix · direction · against/toward
Means "against," "in the way," or "toward": object, observe, obtain, obvious, obstacle, obscure.
Written by Bryan López, English teacher · Updated
Ob- comes from Latin "ob" (against, in front of, in the way of, toward) and signals opposition, blockage, or direction toward something: object = throw against; obstacle = something standing in the way; obvious = directly in the way of the eye (impossible to miss); observe = watch toward; obtain = hold toward (reach and grasp); obstruct = build in the way. It generates a very large number of Latin-based English words.
Like ad-, the prefix ob- assimilates to the following consonant: oc- before c (occur = run against/into, occasion); of- before f (offer = bring toward, offend = strike against); op- before p (oppose = place against, opportunity = at the advantageous approach). The resulting double consonant is the signal: occur (ob+cur), offer (ob+fer), oppose (ob+pose).
Assimilates to the following consonant, producing several surface forms:
Pronunciation: /ɒb/ (stressed) or /əb/ (unstressed). Spanish cognates: object/objeto, obstacle/obstáculo, obvious/obvio, observe/observar, obtain/obtener, obscure/oscuro, obstruct/obstruir. Assimilated forms: oc- (occur), of- (offer, offend), op- (oppose, opportunity).
ob-/ɒb/ /əb/
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Just as ad- assimilates in affect (ad+fect) and arrive (ad+rive), ob- assimilates before certain consonants: ob + cur = occur (b → c), ob + fer = offer (b → f), ob + pose = oppose (b → p). The double consonant at the start of the base word is the assimilation signal. Recognising these hidden ob- words reveals their meaning: occur = run against/into; oppose = place against; opportunity = a favourable approach.
A trick to remember it
Ob- = against, in the way, toward. Massive Spanish cognates: object/objeto, obstacle/obstáculo, obvious/obvio, observe/observar, obtain/obtener, obscure/oscuro. Hidden assimilated forms: oc- (occur, occasion), of- (offer, offend), op- (oppose, opportunity).
Exercise 1 · Form the word
Exercise 2 · Pick the right one
Which word hides assimilated ob- inside it?
The prefix ob- means "against," "in the way," or "toward": object, observe, obtain, obvious, obstacle, obscure. In Spanish it usually maps to ob-.
The prefix ob- is pronounced /ɒb/ /əb/. For example, "object".
"ject" becomes "object". It is a typical example of the ob- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.