Why is it a uniform but an umbrella?

The usage of "a" or "an" depends on the SOUND of the beginning of a word, not the actual letter used. Umbrella begins with the sound "uh". So you use an. Uniform actually begins with the SOUND "YOU" (a long u sound) which starts with a y if you spell the sound of it, so you use a. If the first SOUND starts with a consonant, if you spell it out, you use a. If the first SOUND starts with a vowel, you use an. Examples: A yolk. An egg. A car. An elephant. A bug An igloo. A bat. An orange. See the Related Link.