Exam English

Cambridge C1 Word Formation: Build the Right Form

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Consider this sentence:

The report uses the formal term ______ for whether the policy produced its intended effect, separate from its cost. EFFECTIVE

A weak strategy is to choose efficacy merely because it sounds more advanced. Here, the definition and the contrast with cost license that answer. In a bare phrase such as the effectiveness or efficacy of the policy, both nouns can work. The sentence needs enough meaning to decide. Efficacy asks whether the policy produced its intended effect, not whether it used time or money efficiently.

That three-step check—slot, form, meaning—is the core decision in Cambridge C1 Reading and Use of English Part 3, Word formation. The current paper has eight gaps. A prompt word appears at the end of each line and must be changed to complete the sentence correctly. There are eight questions, worth one mark each.

For more task-specific practice, visit the Cambridge C1/C2 vocabulary hub. The Exam English hub connects this task with the other exam families.

Start with the empty slot

Do not begin by listing every suffix you know. Read the frame around the gap.

  • An article such as a or the may signal a noun.
  • A noun after the gap may require an adjective.
  • A verb may need an adverb beside it.
  • Was plus a gap may need an adjective or a past participle.
  • The sentence may require negative meaning even when there is no visible not.

Then ask what the sentence actually claims. A grammatically neat form can still be wrong in meaning.

Six useful families and boundaries

Efficacy and effectiveness

Efficacy is an uncountable noun for whether something produces its intended effect: the efficacy of the programme or efficacy in reducing errors. Effective is the normal adjective. Effectiveness is the broader, safer noun in general prose. The terms overlap, but efficacy often signals a measured, evidence-led question.

Do not confuse efficacy with efficiency, which concerns speed, cost, or resource use. A slow programme may have high efficacy if it achieves its intended result.

Detrimental and adverse

Detrimental is a formal adjective meaning harmful: detrimental to trust or a detrimental effect on trust. The related noun detriment is useful for recognizing the family.

Adverse overlaps, especially before nouns such as effect, reaction, or conditions. Do not invent a severity rule. Neither word alone says the harm was intentional, permanent, or extreme.

Prevalent and pervasive

Prevalent means widespread or common in a group, place, field, or period: prevalent among new users or prevalent in the sector. Pervasive can suggest that something spreads through many parts of a system. The boundary is gradual, and both may fit some contexts.

Prevalent is not the same as predominant. A practice can be common without being the main practice among alternatives. In word formation, never create a derivative just because it looks regular; the sentence and the supplied family must support it.

Proliferate and spread

Proliferate is usually an intransitive verb: tools, versions, claims, or organisations proliferate. The noun proliferation names the increase. It often suggests a great or rapid growth in number or amount, but it is not automatically negative.

Spread focuses on extension across people or places. One unchanged message can spread without many new messages being created. The meanings can overlap, so context must do the work.

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Ambiguous and equivocal

Ambiguous describes language, data, or a situation that supports more than one reasonable reading. The noun is ambiguity; the adverb is ambiguously; unambiguous means only one reading is available.

Equivocal can imply deliberate evasion. Do not use it merely because wording is unclear. Ambiguous itself says nothing about intent. It also differs from ambivalent, which describes a person's mixed feelings.

Substantial and significant

Substantial means large or important in amount, degree, or extent: a substantial reduction or substantial evidence. The adverb is substantially.

Significant may mean important, large, or statistically meaningful in a stated analysis. It overlaps with substantial in ordinary prose. Do not assume that either word proves certainty, cause, permanence, or statistical significance.

Worked eight-gap text

This original practice text uses only family forms introduced above.

A city tests cooler bus shelters

A city transport team tested shaded panels at twelve bus stops during the summer. The report used the formal term (1) ______—rather than the broader noun effectiveness—for whether the panels achieved their intended cooling effect, considered separately from cost and installation time. EFFECTIVE

Early readings were promising. However, the team warned that a rapid rollout could have a (2) ______ effect on visibility if panels were placed too close to the road. DETRIMENT

Private shade devices had become prevalent in the area, and their sudden (3) ______ had already narrowed some pavements. PROLIFERATE Survey instructions were also (4) ______ about whether passengers should rate heat inside or outside the shelter. AMBIGUITY The revised question was deliberately (5) ______: it asked only about the temperature under the roof. AMBIGUOUS

After the wording changed, response numbers rose (6) ______. SUBSTANTIAL The extra data reduced the remaining (7) ______, though it did not prove that every stop needed the same design. AMBIGUOUS The final report recorded a (8) ______ amount of usable data—more than 10,000 readings—while still recommending a longer trial. SUBSTANCE

Answer key: slot, form, meaning

Gap Answer Sentence slot Required form Required meaning
1 efficacy After the formal term Uncountable noun The sentence defines whether the panels achieved their intended cooling effect, separate from resource use.
2 detrimental Before effect Adjective Harmful to visibility. The word does not claim extreme or permanent harm.
3 proliferation Head of their sudden ... Noun A large increase in the number or amount of devices.
4 ambiguous Complement after were Adjective The instruction supported two readings: rate heat inside or outside.
5 unambiguous Complement after was Negative-prefix adjective Only one reading remains. This is the polarity trap: ambiguous would reverse the stated result.
6 substantially Modifies rose Adverb The rise was large in degree. Substantial cannot directly modify the verb here.
7 ambiguity Object of the remaining Noun The remaining quality or instances of multiple possible readings.
8 substantial Before amount Adjective The exact count shows a large amount of usable data. The following limit prevents a certainty claim.

Notice that prevalent appears in the text but is not forced into an unsupported made-up family form. Word families are not perfectly regular. The task rewards the form that English uses, not the form a suffix chart predicts.

Weaker and more precise analysis

Weak: Gap 6 needs substantially because it sounds academic.

More precise: The gap modifies the verb rose, so it needs an adverb. Substantially is the supported adverb and means that the increase was large in degree.

The second explanation can be checked. It identifies grammar and meaning. That same habit helps when two family members are both real words.

Common mistakes

  • Looking only at the prompt word and ignoring the sentence slot.
  • Adding a negative prefix because the topic sounds negative. Polarity comes from the sentence.
  • Writing efficacy as an adjective or pluralising it in ordinary use.
  • Writing detrimental for instead of the standard detrimental to frame.
  • Treating proliferate as transitive: write new tools proliferated, not the company proliferated new tools in the taught frame.
  • Calling a person's mixed feelings ambiguous; the usual word is ambivalent.
  • Reading substantial as proof of cause or certainty.

Quick check

Complete each sentence and name the clue that controls your answer.

  1. The new logs did not remove every ______ in the original report. AMBIGUOUS
  2. The number of duplicate requests fell ______ after the form was simplified. SUBSTANTIAL
  3. The review found no evidence that the change was ______ to access. DETRIMENT
  4. The rapid ______ of unofficial guides made version control harder. PROLIFERATE

Answers: ambiguity (noun slot), substantially (adverb modifying fell), detrimental (adjective plus to), and proliferation (noun after the rapid).

Fresh practice

Write an 80–100-word paragraph about a school testing a new timetable. Add eight gaps with prompt words. Include one negative-prefix decision and one adjective/adverb decision. For every answer, write three short notes: slot, form, and meaning. If a family form is unfamiliar, check it rather than building it by analogy.

Sources

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