Function words: the small words that hold sentences together
Lesson 3 of 41 in the Test Ninjas TOEFL course: Complete the Words, Reading. In Complete the Words, many gaps are small words: of, the, as, had, his, because.
Test Ninjas Research · Updated October 1, 2026
Lesson at a glance
Detail
This lesson
Module
Complete the Words (Reading)
English focus
Prepositions, articles, determiners, subordinators and auxiliaries: what each small word does and what must come after it
Task skill
Predicting the missing word from the words on both sides of the gap, then confirming it with the prefix and the blank count
Time
About 50 minutes
Access
Included in the TOEFL plan
What this lesson teaches
In Complete the Words, many gaps are small words: of, the, as, had, his, because. They carry grammar, not topic, so you can predict them from the words on both sides of the gap, often before you know what the paragraph is about.
This lesson teaches five families of small words, what each one must have after it, and a four-step way to read any gap: left side, right side, letters, meaning.
By the end of the lesson, you can
Name the five families of small words (preposition, article, determiner, subordinator, auxiliary) and choose the right one from what is around it: usually a noun phrase after a preposition, a clause (subject + verb) after a subordinator, and a verb form after an auxiliary.
Keep the promise each small word makes: a singular or plural noun after a determiner, because before a clause but because of before a noun phrase, had + past participle for the earlier of two past events, and be + past participle for the passive.
In a Complete the Words paragraph, predict each missing word from both sides of the gap before you type, then confirm it with the letters shown and the number of blanks.
What’s inside
Around the 3 teaching cycles below, the lesson opens with a quick check and closes with applied practice, a Check and a debrief. How every course lesson is built.
Teaching cycles in lesson 3
Cycle
Focus
What it teaches
Drills
Cycle 1
English
Five families of small words
8
Cycle 2
English
What the small word asks for next
7
Cycle 3
Task skill
Predicting the missing word from both sides
7
Word bank
The 10 words and phrases this lesson teaches. They come from the real course questions you practice on in the Apply step, so you meet each one again in context.
a series of noun phrase (+ plural noun; the verb agrees with series)
a number of similar things that come one after another
The library is hosting a series of short talks on study skills this month.
Goes with:
a series of talks / tests / events
Word family:
series (noun: the same form for one and for many)
rapid adjective
happening very quickly
The town saw rapid growth after the new rail line opened.
Goes with:
rapid growth, rapid change
Word family:
rapidly (adverb); rapidity (noun)
boundary noun
a line that marks the edge of an area
The river forms the boundary between the two counties.
Goes with:
the boundary between A and B
Word family:
boundaries (plural); bounded by (participle: bounded by the river)
detect verb
to notice or discover something that is hard to see
The sensor detects movement and turns on the hallway lights.
Goes with:
detect changes / movement / signs
Word family:
detection (noun); detector (noun: a device)
dense adjective
with many things or people close together
Traffic downtown is dense between five and six in the evening.
Goes with:
dense traffic, a densely populated area
Word family:
density (noun); densely (adverb)
cross section noun
the surface you see when you cut straight through something
The textbook shows a cross section of a volcano, from the crater down to the magma chamber.
Goes with:
a cross section of + noun
Word family:
cross-sectional (adjective); section (noun)
porous adjective
full of tiny holes that let water or air through
Rain soaks quickly into porous rock such as sandstone.
Goes with:
porous rock, porous material
Word family:
pore (noun: a tiny hole); porosity (noun)
drought noun
a long time with little or no rain
During the long drought, the town asked residents to water their lawns only at night.
Goes with:
a long / severe drought
Word family:
droughts (plural); drought-resistant (adjective)
allow verb
to let someone do something; to make something possible
The new pass allows students to ride any city bus for free.
Goes with:
allow someone to do something
Word family:
allowance (noun); be allowed to (passive)
unusually adverb
more than is normal or expected
The campus was unusually quiet on the first morning of spring break.
Goes with:
unusually high / low / quiet
Word family:
usual (adjective); unusual (adjective); usually (adverb)
The takeaway: Before you type, read both sides of the gap: the small word has to fit what comes before it and what comes after it.
In the full course
Function words: the small words that hold sentences together is part of the full TOEFL course
Unlock all 41 lessons with the TOEFL plan, or try one of the free lessons first.
✓All 3 teaching cycles of this lesson, with 22 drills and feedback on every answer
✓The 10-word bank, each word with a recall drill
✓A walk-through, guided practice and a Check on Complete the Words