What does the doubling rule refer to?

The doubling rule pertains specifically to the practice of doubling a consonant when adding a vowel suffix to a word. This occurs to maintain the correct pronunciation of the original word, particularly when it is a short vowel followed by a single consonant at the end of a syllable. For instance, in the word "run," when adding the suffix "-ing," it becomes "running," where the final 'n' is doubled to preserve the vowel sound.

This rule is fundamental in English spelling and helps ensure that words are pronounced correctly. Understanding this rule enhances accuracy in writing, as it indicates when a consonant must be doubled to follow standard conventions of the language. Other options do not accurately describe this specific rule as they either address different aspects of spelling or refer to situations not governed by the doubling rule.