# Usage of an **URL:** \ **Category:** Factual Questions\ **Created:** [August 8, 2001, 5:53am UTC](https://boards.straightdope.com/t/usage-of-an/75420 "2001-08-08T05:53:00Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![KwikStah](https://avatars.discourse-cdn.com/v4/letter/k/e47c2d/32.png) [@KwikStah](https://boards.straightdope.com/u/KwikStah)\ **Post date:** [August 8, 2001, 5:53am UTC](https://boards.straightdope.com/t/usage-of-an/75420/1 "2001-08-08T05:53:00Z")
In a discussion about statistics, my friend said, “I used _an_ SRS of 1,000.” SRS stands for Simple Random Sample, so wouldn’t one say “a SRS,” or is there a rule that one must use an with acronyms, or letter names, e.g. “He drives an S500.” ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [August 8, 2001, 5:59am UTC](https://boards.straightdope.com/t/usage-of-an/75420/2 "2001-08-08T05:59:51Z")
The rule is quite simple. If the next word starts with a vowel sound, then “an” is the proper word. Notice that I said “vowel sound”. “S” is pronounced “ess”, so even though it’s not a vowel, it starts with a vowel sound. Similarly, “hour”, while not starting with an actual vowel, still takes the article “an” because the “h” is silent. Words such as “yolk” and “historian”, however, do not take the article “an”: “y” in this case is not acting as a vowel, and the “h” is not silent. ---
**Author:** ![Goldeneldon](https://avatars.discourse-cdn.com/v4/letter/g/f19dbf/32.png) [@Goldeneldon](https://boards.straightdope.com/u/Goldeneldon)\ **Post date:** [August 8, 2001, 6:02am UTC](https://boards.straightdope.com/t/usage-of-an/75420/3 "2001-08-08T06:02:52Z")
I would think that the usage of “an” is determined by the proceeding sound not the character. If it is a vowel then you use “an”, if not then “a”. in “SRS” the “S” is pronounced “Es” making it a vowel sound. Maybe somebody could clarify this for me.