Grade by Grade
B. Foundations of Language · Handwriting, Spelling and Sentences

Prefixes: Across, Between, Against and More

B2.1 B2.2About 40 minutes
Learning goals
  • I can tell the meaning of the prefixes super-, inter-, anti-, trans-, semi-, multi-, fore-, de- and ex-.
  • I can use the not prefixes in-, im-, il- and ir-, and choose the right one.
  • I can spell words with prefixes, including ones with double letters, like illegal.
  • I can figure out a new word by adding the meanings of its parts.

Words to know

prefix
A word part added to the beginning of a base. It changes the meaning.
base
The main part of a word that carries its meaning.
morpheme
The smallest part of a word that has meaning: a prefix, a base or a suffix.
word sum
A way to show a word's parts, like inter + nation + al = international.

Remember from Grade 3

You know lots of prefixes: un-, re-, dis-, mis-, pre-, non-, over-, under-, in-, im-, sub-, mid-, uni-, bi- and tri-. You learned that a prefix doesn't change the spelling of the base: mis + spell = misspell.

In Grade 4 you will learn prefixes that show up in science, social studies and math words. They will help you read and spell big words, like international and transportation.

PrefixMeaningExamples
super-above, more than, extrasuperhero, superstar, superhuman
inter-between, amonginternational, interact, intersection
anti-againstantibacterial, antifreeze
trans-across, changetransport, translate, transform
semi-half, partlysemicircle, semifinal, semicolon
multi-manymulticoloured, multicultural, multimedia
fore-before, at the frontforecast, forehead, foresee
de-remove, undo, downdefrost, decode, deflate
ex-out, out ofexit, export, exhale
Grade 4 prefixes
Worked example

Let's figure out "international"

What does international mean in Toronto has an international airport?

  1. Find the parts: inter + nation + al.
  2. inter- means between. A nation is a country. -al means related to.
  3. Put the meanings together: related to travel between countries.
  4. Check in the sentence: an airport with flights to and from other countries. That makes sense!

international means between or among nations (countries).

The four ways to say "not"

The prefix that means not changes its spelling to match the first letter of the base. This makes the word easier to say.

  • in- before most letters: incorrect, invisible, incomplete
  • im- before b, m, p: impossible, impolite, imbalance
  • il- before l: illegal, illogical
  • ir- before r: irregular, irresponsible
im+possible=impossiblebefore b, m, pil+legal=illegalbefore lir+regular=irregularbefore rin+correct=incorrectmost other letters
The not prefix changes to match the first letter of the base. The base never changes, so il + legal keeps both l's.

Double letters

A prefix never changes the base, so il- + legal has two l's: illegal. ir- + regular has two r's: irregular. The same thing happens with inter + rupt = interrupt and dis + satisfied = dissatisfied. If you see a double letter where a prefix meets a base, it's probably right!

ir+replace+ablenotbasecan beirreplaceable = cannot be replaced
A word sum for irreplaceable. Each part adds meaning. The prefix ir- means not, the base is replace, and the suffix -able means can be.
Worked example

Let's build and spell "irresponsible"

Spell a word that means not responsible.

  1. The base is responsible. It starts with r.
  2. The not prefix before r is ir-.
  3. Write the prefix, then the whole base, with no letters dropped: ir + responsible.

irresponsible (two r's: one from ir-, one from responsible).

Prefix or not?

Not every word that starts with these letters has a prefix. Test it: take off the letters. Is a real base left that fits the meaning? antelope starts with ant, a bit like anti-. Take off ante and you get lope. Does against lope mean anything? No! antelope is just the name of an animal. Always check the meaning.

Prefixes in other subjects

  • Science: antibacterial soap works against bacteria. To defrost the freezer means to remove the frost.
  • Math: a semicircle is half a circle. Multi- in multi-digit means many digits.
  • Social studies: transportation carries people and goods across places. Canada is a multicultural country: people from many cultures live here.
A funny-but-true fact

Sneaky fact: the word prefix has a prefix! pre- means before, and fix means attach. So a prefix is a word part that is fixed on before the base.

Hands-on activity

Prefix flip book

You need: 2 or 3 sheets of paper, scissors (with a grown-up's help), a stapler or tape, and a marker.

  1. Cut a sheet into 6 small strips. On each, write one prefix: inter-, trans-, semi-, multi-, de-, ex-.
  2. On a longer strip, write bases: port, act, circle, colour, frost, code, plain, form.
  3. Staple the prefix strips on the left of a page and the base strips on the right, so you can flip each one separately.
  4. Flip to make real words: transport, interact, semicircle, multicolour, defrost, decode, explain, transform. Write each word you make and its meaning in your own words.
  5. Flip to make silly words too (semifrost!) and invent a meaning. Is it a real word? Check a dictionary.

Grown-ups: help with the scissors and stapler.

Your turn

1

What does semicircle mean?

2

What does intersection mean? (Hint: section means a part.)

3

What does defrost mean?

4

Add a not prefix to legal. Spell the new word.

5

Add a not prefix to regular. Spell the new word.

6

What does multicoloured mean?

7

A weather forecast tells about the weather when?

More practice: warm-up

1

What does super- mean?

2

What does anti- mean?

3

What does ex- mean in exit?

4

What does trans- mean?

5

What does multi- mean?

More practice: on your own

1

Spell the word that means not responsible. Explain the spelling.

2

Spell inter + rupt. What does interrupt mean? (rupt means break.)

3

What do you think transport means? (port means carry.)

4

What do you think antibacterial soap does?

5

Which not prefix goes with polite: in-, im-, il- or ir-? Explain.

Challenge

1

Use the word sum to explain irreplaceable: ir + replace + able.

2

Is foreign made of fore- + ign? Explain how you know.

3

Make two real words with trans- and two with inter-, and tell what each means.

Check your understanding

Quiz

1.

What does the prefix inter- mean?

2.

A semifinal game is...

3.

Which word is spelled correctly?

4.

Which prefix means not in irregular?

5.

What does exhale mean? (hale comes from a word meaning breathe.)

6.

Which word has a real prefix?

For parents and teachers

Big idea: The Grade 4 Ontario Language curriculum (B2.1) asks children to use knowledge of the meanings of words and morphemes (bases, prefixes and suffixes) to read and spell words, and B2.2 (vocabulary) asks them to understand and use new words in various contexts, including other subjects. These Grade 4 prefixes appear in many science, math and social studies words.

How to help at home:

  • When you meet a long word together, ask: "Do you see a prefix? What's the base? What do they mean together?"
  • Point out prefixes in the world: EXIT signs, SUPERmarket, antiFREEZE, the weather forecast.
  • Praise the double-letter logic: illegal, irregular, interrupt.

Common difficulties:

  • Dropping a letter where prefix meets base (ilegal, iresponsible). Write the prefix, then the whole base.
  • Choosing the wrong not-prefix. Look at the base's first letter: b/m/p → im-, l → il-, r → ir-, otherwise in-.
  • Seeing prefixes that aren't there (foreign, antelope). Check that the parts make sense together.
  • Note: in- can also mean in or into (inside, input), so meaning always comes first.