The vowel “U” is a bit unique because it has two Long-vowel sounds. The two sounds are very similar, but they are used in different situations. So, how do you know which one to choose?

It all depends on which letter comes just before the Long-U.

Long-U-2 (/uw/)

Long-U-2 is used after sounds that are made with the front part of the tongue. This includes: T / D / L / N / S / R / TH / J. Here are some examples: tune / duty / elude / nuclear / suit / rule / enthused / June.

Long-U-1 (/yuw/)

Long-U-1 is used after any sounds that are not made with the front part of the tongue. This includes: P / B / F / M / K / G / H / “none”. Some examples are: pupil / bugle / fuse / music / cube / argue / huge / use.

Exceptions

In English there are always exceptions, and in this case the exceptions happen with some Long-U-2 words.

• Some words with a “T” or “N” can also be pronounced with Long-U-1. Some examples — pronounced both ways — are: tune / tube / avenue / news. Now, the second way (with Long-U-1) sounds more old-fashioned, like the way some elderly people speak. So, following the rule keeps it more simple for you. But be aware that you may hear some people say a few words the other way, so don’t let it confuse you.
• There is a handful of words with “L” and “N” that always go against the rule, and use Long-U-1. You should memorize these ones: volume / value / evaluate / menu / January / monument.

Does it really matter which one you use?

It can. Especially when you accidentally use Long-U-2 in place of Long-U-1.

• There are some words that can be confused. For example, if you want to say the word “use” but you pronounce it with Long-U-2 instead of Long-U-1, then you will end up saying the word “ooze”. Likewise, “hue” would sound like “who”.
• Even if there is not a word that could be confused, using the wrong sound could make you unclear. For example, if you try to say a word such as “huge” or “pupil” with the wrong sound, others may not understand what you are talking about.
• With bigger words, other people will probably still understand you. So if you try to say “regular”, “computer” or “document” with Long-U-2 (instead of Long-U-1), it will sound like a mistake, but most of the time others will know what word you are trying to say.

Another phenomenon

There is a group of words that have a sound change when a “T” or “D” comes before a Long-U-1. For example, in a word like “actual”, the “T” gets combined with the “Y” part of Long-U-1 (/yuw/) and turns into a “CH” sound. Likewise, in “graduate” the “D” combines with the “Y” and makes a “J” sound. There are quite a few words like this, such as: statue / costume / situation / punctuate / virtual / individual / schedule.

However, this is a phenomenon that does not only happen with Long-U. These words are part of a bigger pattern, and will be the topic of a different post.