Why do you double 'n' in the word 'beginning' but not in 'opening'?

The correct answer highlights an important phonetic and orthographic principle in English spelling: the doubling of the final consonant in a word when forming the present participle or gerund form is often dependent on syllable stress patterns.

In the case of "beginning," the base word "begin" ends with a single vowel followed by a single consonant. When adding the -ing ending to "begin," the final consonant is doubled because the stress is on the second syllable (be-GIN). This rule applies because the last syllable of the word is stressed, which requires the consonant to be doubled in order to maintain that stressed syllable as a closed syllable. The doubling serves to signify that the preceding vowel (the 'i') is short.

Conversely, in the word "opening," the base word "open" also ends with a vowel and a consonant, but adding -ing does not require the final consonant to be doubled. The stress in "open" falls on the first syllable (O-pen), which shifts the phonetic structure and context. As the last syllable is not stressed, it retains its single consonant without modification.

Thus, understanding the relationship between syllable stress and conson