"Can the context of a word change the way its syllables are stressed/unstressed? Myra"

Yes, Myra, the context can definitely change the way we stress the syllables. Here's a simple example:

"I would never desert you in the desert."

How did you stress the syllables in the word "desert"? Hopefully, the first time the word showed up, you pronounced it "de-SERT," with the stress (accent) on the second syllable. But what about the second appearance of the word? You didn't pronounce it the same way, did you? You pronounced it "DES-ert," with the accent on the first syllable.

The difference, of course, is that even though they are spelled the same, these are two quite different words. One of them is a verb, that means to abandon, and the second is a noun -- a dry and barren landscape.

There are occasions when a single word functions as either a noun or an adjective, depending on the context, and the difference in part of speech is reflected in the way it is pronounced. For example, consider the word "arithmetic." Is it a noun? Or is it an adjective? It actually could be either, depending on the context.

"I really enjoy studying arithmetic."

In this case, "arithmetic" is a noun, a branch of mathematics, and we pronounce it "a-RITH-me-TIC," with the primary accent on RITH, and a secondary accent on TIC.

"I really enjoyed studying an arithmetic sequence."

In this case, "arithmetic" is an adjective rather than a noun; it is describing a type of sequence. As an adjective, the word is pronounced "A-rith-ME-tic," with the stresses inverted from the noun pronunciation.

Can you think of other words that have different pronunciations depending on the context?

Incidentally, there's another way that context can affect how syllables are stressed. Sometimes, the innate rhythm of a phrase we're saying can lead to slight variations in accent. I emphasize here the word slight.

Here's one example. I mentioned the word "sequence" above; let's take that word and make it plural: "sequences." If you pronounce this word, you will likely pronounce it like this: "SEQ-uenc-es," with primary stress on the first syllable, and no secondary stress. I checked a phonetic spelling in an online dictionary, and that is exactly what it showed.

So now let's take the phrase "arithmetic sequence" and make it plural: "arithmetic sequences."

How do you pronounce this? The answer (I love combining math and poetry) is that you pronounce it iambically, which means you pronounce it with alternating unstressed and stressed syllables: "A-rith-Met-ic SEQ-uenc-ES."

Your sense of rhythm almost begs you to put a secondary stress on that final syllable. Now, as I said, it's very slight, and maybe you don't add that extra stress yourself, but I can tell you, as a math teacher, I hear that extra accent all the time. The same is true for the phrase "geometric sequences."

The same thing happens (for essentially the same reason) when we read poetry. Say the word "happy" and ask yourself where the stress is. Presumably you said that it comes on the first syllable: "HAPP-y."

But now read these very familiar lines of poetry: 

But I heard him exclaim, 'ere he drove out of sight,
"Happy Christmas to all, and to all a good night!"

Did you notice what happened? Your brain subconsciously (or maybe consciously) got so wrapped up in the rhythm of unstressed/unstressed/STRESSED over and over again that you really didn't give stress to either syllable of "happy," waiting instead to punch the first syllable of "Christmas."

In fact, that's precisely what the author intended you to do; it is a form of poetry called "anapestic tetrameter," in which every stressed syllable is preceded by two unstressed syllables. And those two unstressed syllables are the word "happy."

Related post: How to recognize stressed and unstressed syllables.

Wanshika from SriLanka asks, how to "identify stressed and unstressed vowels without pronouncing them loudly?"

That's a good question, Wanshika, and both Mr. and Mrs. Puzzler have an answer for you.

Mrs. Puzzler says, "Tap your hand on a desk for each stressed syllable." (Or, if you're trying to be extra quiet, tap on your leg!). What you'll find is that it's almost impossible to tap on the unstressed syllables; your brain somehow pushes you into doing the tap whenever your vocal chords are forming a strong syllable.

Mr. Puzzler says, "Tap on your leg with your thumb and your forefinger. If you're like me, you'll find that you gravitate toward tapping with your thumb on the stressed syllables, and the unstressed syllables with your forefinger." Mr. Puzzler's suggestion is really better for checking rhythms of poetry, if you already know where the accents are supposed to be.

If you try to tap this sentence out on thumb and index finger, then you'll find it has a perfect meter from the start to ending syllable.

[Note: the sentence above is written so that the first syllable is accented, and then it alternates between stressed and unstressed].

Related post: How context affects the way we stress syllables.