Replies

According to the many sources I use regularly, "a historical" is grammatically correct as, although many people drop the "h" when speaking, the "h" is not silent. "A historically" is also the generally accepted and generally used form.

An excerpt from thesaurus.com explains it well:

An Historic vs A Historic

Traditionally, the word an is used as an article before vowel sounds and the word a is used as an article before consonant sounds. For example, we would say an apple and a banana. However, we would also say an hour and a university. The word hour has a silent H and begins with a vowel sound, so we use the word an. The word university begins with a consonant “yoo” sound and so we use the word a.

It’s perfectly acceptable and natural sounding to use a before the word historic as in This is a historic event. The word historic doesn’t have a silent H and begins with a consonant sound like the word hip, so it makes sense to use the word a. Additionally, most style guides recommend using a before historic, history, and historical.