From thorough description to elaborate speech and diction, combinations of words and their placement in sentences can express a variety of emotions in any number of situations. One of the simplest but most effective techniques is the use of the interjection, which is a part of a sentence that is independent from the rest of the sentence grammatically.
An interjection is most often a short word or phrase placed in a sentence specifically to show emotion. For example, "Ouch!" expresses surprise and pain. "Hey!" is another term that can express a few different emotions, from surprise to disappointment, or even excitement. The word "uh" can express confusion or discomfort, or even imply stupidity.
This term is rooted in Latin, and closely translates to "thrown into the middle." Therefore, a reader will very often find an interjection in the middle of a sentence. It does not necessarily have to be just one word. Here are some examples:
I crossed the parking lot and — wouldn't you know it! — I forgot my keys inside the building.
The phrase "wouldn't you know it!" does not grammatically relate to the other parts of the sentence, but placed in the middle of that sentence, it expresses a sense of irony or even humor.
Because the definition of interjection does not specifically cite any specific emotion, many linguists believe one word sentences such as "hello" or "yes" can be considered an element of this part of speech as well:
Hello. My name is Doctor Richards.
Yes. I did bring my prescription.
Yes! We won!
This latter example might be considered two interjections: the first, "Yes!" expresses a positive excitement, while "We won!" expresses excitement, positivity, and a specific reason for the excitement. These words are often followed by some sort of punctuation, such as a period to end the sentence or, in many cases, a comma to continue the sentence. Because the term is separated from the rest of the sentence, there must be some sort of punctuation to indicate a pause or stop. Words that act as interjections in some scenarios therefore may not fulfill the same role in other cases.
A simple hello would have sufficed.
While the word "hello" acted as an interjection in the earlier example, in this case, it is not separated from the rest of the sentence and therefore does not act as one.