Requires a combining vowel for attachment when it begins with consonant?

The letter "h".

The letter "h" is one of the few letters in the English alphabet that requires a combining vowel when it begins a word or syllable. This is because the letter "h" is not a vowel itself, and therefore cannot stand alone to create a syllable.

For example, the word "hat" is pronounced with a long "a" sound, and the word "hen" is pronounced with a short "e" sound. In both of these words, the letter "h" is followed by a combining vowel, which is the letter "a" in "hat" and the letter "e" in "hen".

There are a few exceptions to this rule. For example, the word "hour" is pronounced with a long "oo" sound, and the word "honor" is pronounced with a long "o" sound. In these words, the letter "h" is followed by a consonant, but the words are still pronounced with a vowel sound.

This is because the letter "h" is sometimes considered to be a semi-vowel, which means that it can sometimes function as a vowel in a word. However, in most cases, the letter "h" requires a combining vowel when it begins a word or syllable.