An “S” or A “S”? Which is correct?

We use an+s when S is pronounced as the letter “s”. We use a+s when a word starts with “s”.

I bought an S-Class train ticket.

I tried to buy a sushi mat at Walmart. 

When to use An + “S” 

We use the article “an” with “S” only when we pronounce the letter “S”. Remember that we use “an” with vowel sounds and the letter “s” is pronounced “ess”. The “e” sound at the beginning of the pronunciation of the letter is the reason why we use ”an”. 

The most common examples that use “an+s” are Abbreviations when they start with “s”.

We need to create an s.o for the Kemper account.

Are you working with an S.O.P?

When to use A +“S”

We use the article a with s for all words that begin with the letter s. We use the article “a” before words that start with “s”. “S” has a consonant sound when it is used as part of a word. 

I picked a strawberry in the field.

I wanted to eat a salmon bagel.