A progressive aspect is a form of expression that indicates an action that is occurring, or was going on at a certain point in time, or will happen in the future. This is used to refer to something that is not necessarily repeated behavior, but only to one particular instance. It also does not necessarily indicate that the activity came to an end, but merely that it was, is, or will occur in a certain context. A progressive aspect in English is typically formed through the use of the auxiliary verb "to be" and a main verb with the suffix "-ing" such as "I am walking to the store."
As the name suggests, the progressive aspect indicates that something is in progress with regard to a certain period in time: past, present, or future. Regardless of the tense, it is typically created through the use of some form of the verb "to be" which is used as an auxiliary verb. An auxiliary verb does not indicate the main action of a sentence, but provides additional information. In this case, it is responsible for creating the progressive aspect and indicates that the main verb, which is the action of the sentence, is happening.
For a progressive aspect in past tense, for example, the auxiliary "was" is typically used as a form of "to be." This can be seen in a sentence like "I was going to the store when you called," which indicates what was happening when another event occurred. The progressive aspect is commonly used in this way, to express that one action was going on at the time that something else happened. It does not necessarily indicate that the action stopped, however, and in that example the subject "I" may still have been going to the store after the call.
In the present tense, the progressive aspect functions in much the same way, but typically uses "is" or "am" as the auxiliary verb. "I am talking on the phone," for example, indicates what the subject is doing right now. An example similar to the one in the past tense would be "He is driving while singing," which indicates one action that is happening in the midst of another event.
The progressive aspect in the future tense functions in much the same way, but uses the auxiliary "will be" with the main verb. For example, "Tomorrow, I will be flying to Ireland," indicates an event that occurs in the future. It does not necessarily provide information about that action stopping or changing, but simply demonstrates something that will happen. It can also be used to indicate events occurring when something else happens, such as "He will be hiking in the forest when you try to call him."