Spelling - Changing 'y' to 'i'


To learn and practise the spelling rules associated with base words ending in 'y' when endings (suffixes) are added.

Lesson plan

The lesson is divided into a series of activities where students group words according to whether they keep the final 'y' of the base word when a suffix is added, or change 'y' to 'i'. For each set of examples, students are asked to identify and make predictions about the patterns for this area of spelling.


The letter y is very often used at the end of a word instead of i, e.g.:

  • duty, plenty, happy, tidy, defy, apply

Let’s see what happens when we add an ending (suffix) to a base word like these:

  • dutiful, plentiful, happiness, tidiness, defiance, appliance

Now the y is no longer at the end and so it is changed to an i.

However, sometimes the y does not change to i. We find examples like tidying and joyful.

When to change and when not to change? In this resource we will explore the patterns behind these spelling differences.

Activity 1

Ask students to look at the set of examples on the slide and sort them into two different groups:

  • CHANGE 'Y' to 'I': the final y of the base word changes to i when the ending is added
  • KEEP 'Y': the final y of the base word does not change when the ending is added

Then, after they have sorted the examples into two groups, ask them if they can see a pattern. When do we change y to i and when do we keep the y? A clue is to look at the first letter of the suffixes (endings).

For advanced students, explore why we might want to keep the y before a suffix starting with i.

Activity 2 Advanced

Look at the next group of examples. None of them involve a suffix starting with i, so we don't need to worry about that exception here. But do they all change y to i?

Ask students to sort them into two groups, as in the previous activity, and find out.

Then, after they have sorted the examples into two groups, ask them if they can see a pattern.

Next, explore some exceptions to this rule.

Activity 3 Advanced

Tell students that we need to look at the special pattern before the -s ending. This ending is used with nouns to form plurals, e.g.:

  • butterfly + -s → butterflies

We also find -s as a verb ending:

  • terrify -s → terrifies

As you can see, before -s the y changes to ie instead of just i. This avoids misleading spellings like terrifis, or cris instead of cries, which would imply the wrong pronunciations.

Ask students to test if this works as a general pattern, and whether we find the same exception that we found before (for the y to i rule), for items where there is a vowel letter before the final y (like boy). To test this, ask students to sort the next set of examples into two groups, CHANGE 'Y' TO 'IE' and KEEP 'Y'.


Finally, explore the following examples which keep the y:

  • the baby’s hat, the spy’s secret, the butterfly’s wings

Here there is no vowel letter before the y. What is going on?

  • These are nouns with the possessive ending, marked with an apostrophe (’) before the s. This ending has a different meaning from the plural ending. For example, the butterfly’s wings has a similar meaning to the wings of the butterfly: the butterfly ‘possesses’ the wings.
  • The possessive noun butterfly’s and the plural noun butterflies sound the same, but they are spelled differently because of their different meanings.


We can now sum up what we have found overall, adding the findings for -s endings to our earlier results.

  • When an ending is added, a final y usually changes:
    • to ie before -s (e.g. babies)
    • to i before other endings (e.g. beautiful).
  • However, it does NOT change:
    • before possessive -’s (e.g. baby’s)
    • when the suffix starts with i (e.g. babying) or
    • when there is a vowel letter before the final y (e.g. employment, employs).

This accounts for numerous examples. However, there are as usual some exceptions to the general pattern! These examples break the pattern by keeping the y:

  • shyness, shyly, slyness, slyly, dryness, dryly (or drily)
  • babyhood, bellyful, ladyship


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