The 1-1-1 doubling rule states that when adding a vowel suffix to a one-syllable word that has one vowel followed by one consonant, you must double the final consonant before adding the suffix.

You double the final consonant when the word is one syllable, has one vowel, and ends with one consonant.

The word 'run' becomes 'running' after doubling the final consonant.

The word 'walk' becomes 'walking' without doubling the final consonant.

The present participle of 'whisk' is spelled 'whisking' after doubling the final consonant.

The past tense of 'test' is 'tested' after doubling the final consonant.

Yes, the word 'play' does not follow the rule; it becomes 'playing' without doubling the final consonant.

A vowel suffix is a suffix that begins with a vowel, such as 'ing', 'ed', or 'er'.

A one-syllable word has only one vowel sound and one syllable, while a multi-syllable word has more than one vowel sound and syllable, which typically does not require doubling the final consonant.

For words ending in 'e', you usually drop the 'e' before adding a vowel suffix, unless the suffix begins with a consonant.