It’s an S. Because the pronunciation of the letter "S" begins with a vowel sound (it sounds like "ess"), we use the article "an".

It’s an S. Because the pronunciation of the letter "S" begins with a vowel sound (it sounds like "ess"), we use the article "an".

Where can I buy a T-shirt with an S on it?

Where can I buy a T-shirt with a S on it?

Remember, the rule for using a or an is based on pronunciation, not spelling.

Can you name a large city beginning with an S?

The population shows an S-shaped growth curve.

Follow the same convention with other consonants that are pronounced with a vowel sound:

• an F
• an H
• an L
• an M
• an N
• an R
• an X

We also use the indefinite article "an" before abbreviations and acronyms that begin with the letter "S" but are pronounced as separate letters, including:

• an SEO (Search Engine Optimization)
• an SLA (Service-Level Agreement)
• an SMS (Short Message Service)
• an SMTP (Simple Mail Transfer Protocol)
• an SSD (Solid-State Drive)
• an STD (Sexually Transmitted Disease)
• an SUV (Sport Utility Vehicle)
• an SVG (Scalable Vector Graphics)