• 4-minute read
• 7th September 2016

Spelling Tips: The Doubling Up Rule

In English, most spelling rules are more like ‘rough guidelines’. But one of the more reliable is the doubling up rule, which we use when adding a suffix to certain words. And in this post, we’re going to explain the basics of how it works.

What Is the Doubling Up Rule?

The doubling up rule tells us that we double the final consonant in single-syllable words that end in a single consonant after a single vowel when adding a vowel suffix (i.e. a suffix that starts with a vowel, like ‘-ing’ or ‘-est’).

The word ‘run’, for instance, is a single syllable in length (i.e. pronounced as one unbroken sound) and ends in a single consonant (‘n’) after a single vowel (‘u’) and another consonant (‘r’). However, when modified with a vowel suffix, we always use a double ‘n’ in the middle (e.g. ‘runner’ or ‘running’).

This applies to any single-syllable word that follows this spelling pattern, including:

‘Y’ can also count as a vowel in this context (like with ‘blur’ and ‘blurry’). However, this rule doesn’t work with words that end in a ‘w’ (e.g. ‘snow’ → ‘snowing’), ‘x’ (e.g. ‘box’ → ‘boxed’) or ‘y’ (e.g. ‘play’ → ‘player’).

Since the doubling up rule applies to words with one syllable and which end in one consonant after one vowel, it’s sometimes known as the 1:1:1 rule.

Multi-Syllable Words

Things get a little more complicated when a word has more than one syllable. On the one hand, plenty of multi-syllable words still require doubling the final consonant when adding a vowel suffix. Typically, these are words that contain a stressed syllable before the final consonant:

On the other hand, there are also some multi-syllable words that don’t require doubling the final consonant when adding a vowel suffix. These are usually words that have an unstressed syllable for the final consonant:

In some cases, whether to double the final consonant depends on the suffix added. ‘Prefer’, for example, gains an extra ‘r’ in ‘preferred’ or ‘preferring’. This is because, in both, the final syllable is stressed. However, no doubling is required in ‘preference’, since the final syllable here is unstressed.

Multi-Syllable Exceptions

There are some words that don’t follow the pattern above, but with which we still double the final letter when adding a vowel suffix to clarify the pronunciation.

With ‘format’, for example, we typically place the stress on the first syllable. But we still double the ‘t’ when adding a suffix to show that it is pronounced with a short vowel sound. Thus, we pronounce ‘formatted’ as ‘for-mat-ed’, not ‘for-mate-ed’, and the double ‘t’ before the suffix helps to clarify this.

To make things more confusing, British English conventionally doubles the final ‘-l’ in some words, but American English doesn’t:

In other words, multi-syllable words can be tricky! Using the pronunciation to guide your spelling will usually help, but don’t forget to check specific words in a dictionary if you’re unsure whether to double the final consonant when adding a vowel suffix. Likewise, it’s important to double check the spelling of multi-syllable words if you’re not completely confident about the spelling.