TOEIC Link Part 5: affect versus effect

Affect and effect sound almost identical in fast speech and differ by a single letter, which is exactly why Part 5 likes to put them in the same answer set. The trick is that they usually belong to different parts of speech: affect is normally a verb meaning to influence or have an impact on something, while effect is normally a noun meaning the result or consequence of a change. The slot's grammar — not your ear — tells you which one fits. For the broader skill of matching the answer to the grammatical role of the slot, see word choice versus word form.

The core rule: action versus result

affect (verb) means to influence or to produce a change in: The new policy will affect every department. / Rising costs affected our margins. / Weather can affect delivery times.
effect (noun) means a result or consequence: The discount had a strong effect on sales. / We are still measuring the effect of the change. / side effects, a positive effect, the effect of the merger.

A memory hook: Affect is an Action (both start with a). Effect is the End result (both start with e). If the slot is doing something, you want the verb affect; if the slot is a thing you can have, measure, or point to, you want the noun effect.

How to read the slot

A verb is needed → affect. If the slot sits between a subject and an object and acts as the main verb, choose affect: Higher fuel prices may (blank) shipping rates → affect.
A noun is needed → effect. If the slot follows an article (a, an, the) or an adjective (positive, lasting, immediate), or comes after a preposition, choose effect: The campaign had an immediate (blank) on traffic → effect.

The fastest test: look at the word right before the blank. The, a, an, or an adjective in front means a noun belongs there — that is effect. A subject (or an auxiliary like will, may, can) in front means a verb belongs there — that is affect.

Common Part 5 traps

The rare reversals. Effect can be a formal verb meaning to bring about (to effect change), and affect can be a noun in psychology (flat affect). These are uncommon in Part 5; the test overwhelmingly uses verb affect and noun effect, so default to those unless the structure clearly forces the rare sense.
Adjectives are the giveaway. A lasting (blank), a noticeable (blank), the overall (blank) — an adjective in front always signals the noun effect.
will, may, can, could flag the verb. A modal or auxiliary before the slot means a verb follows, so you want affect.
Do not choose by sound. The two are near-homophones, so rely on the part of speech the slot demands, not on how the option sounds.

Quick check

Decide whether the slot needs a verb (an action) or a noun (a result), then choose.

The merger will (blank) staffing levels across both offices.
Analysts are still studying the (blank) of the price cut.
Poor weather could seriously (blank) the construction schedule.
The training had a measurable (blank) on error rates.

Answers: 1. affect (verb, main action) 2. effect (noun, after the) 3. affect (verb, after could) 4. effect (noun, after a measurable).

The takeaway

Affect and effect differ by one letter and one part of speech, so ignore the sound and read the structure: when the slot is the main action between a subject and an object, you want the verb affect, and when it follows an article or adjective and names a result, you want the noun effect. Check the word immediately before the blank and the answer usually settles itself. For more pairs where structure decides the answer, see precede versus proceed and accept versus except.