TOEIC Link Part 5: credible versus credulous

Credible and credulous both descend from the Latin credere, "to believe," yet they sit on opposite sides of the act of believing. Credible describes something worth believing; credulous describes someone too willing to believe. Because the two adjectives look almost identical and share a root, Part 5 likes to drop either into a blank and reward the reader who checks whether the sentence is praising a source or criticizing a listener. For another pair of look-alike adjectives built on one shared stem, see economic versus economical.

The core rule: believable versus easily fooled

• credible (adjective) = believable, trustworthy, deserving of belief. The witness gave a credible account. / The report cites credible sources.
• credulous (adjective) = too ready to believe, gullible, easily deceived. A credulous investor fell for the scheme. / Don't be so credulous about online reviews.

The memory hook: credible ends like reliable and dependable — adjectives that mean "worthy of" the action. Something credible is worthy of belief. Credulous ends like nervous and anxious — adjectives that describe a person's disposition. A credulous person is disposed to believe too quickly.

Why Part 5 likes this pair

Both words are adjectives, so the grammar slot is identical. What the adjective modifies is your clue.

The auditor accepted the figures only after confirming they came from a __ source.

A source worth trusting is being praised, so the answer is credible.

Scammers target __ consumers who accept claims without checking them.

Consumers who believe too easily are being criticized, so the answer is credulous.

Spotting the clue in the structure

Look at what the blank describes:

• It describes information, a source, a story, or a person being believed (a credible explanation, a credible witness, a credible threat) → choose credible.
• It describes a person doing the believing, usually with a negative tone (a credulous audience, credulous buyers, the credulous public) → choose credulous.

Watch the collocations the test reuses: credible evidence, a credible alternative, and a credible deterrent all praise something as believable, while credulous almost always attaches to the people who are taken in. If you can replace the word with "trustworthy," it is credible; if you can replace it with "gullible," it is credulous. For another pair where one word praises and the look-alike warns, see eminent versus imminent.

Quick self-check

1. The company's safety claims were backed by __ third-party testing. (credible — believable, trustworthy)
2. The fraud succeeded because it targeted __ first-time investors. (credulous — too ready to believe)

Takeaway

If the blank describes information or a source as worth believing, choose credible. If it describes a person who believes too easily, choose credulous. The shared root credere is the trap; check whether the sentence praises what is believed or criticizes who is doing the believing, and the ending — -ble for "worthy of," -ous for a disposition — confirms it.