Tense
A famous comment about the difficulty of thinking about time is usually attributed to Saint Augustine (354–430 AD): ‘What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.’ We could make a similar observation about the two linguistic categories in which information about time is presented, tense and aspect. The first of these categories, tense, is a familiar part of the way we talk about English grammar: one does not need to have studied very much grammar to know that Jane runs is usually described as present tense, Jane ran as past, and Jane will run as future. It also seems to make perfect sense for a language to mark differences in the temporal location of different events.
But the picture gets more complicated when we look at the details of the way these different verb forms actually work in English. Tenses are very good examples of prototype categories: their meanings can be defined by specifying the central tendency of their members, but we find many peripheral instantiations of the category which lack the prototypical features. These central tendencies are often the meanings suggested by the grammatical label for the tense-marker in question. But it soon becomes apparent that the labels ‘past’, ‘present’ and ‘future’ can be quite misleading as descriptions of the time-reference of some uses of English verb forms. For example, take the English present tense, as exemplified by forms like Jane runs or Jane is running. These are both examples of the present tense; runs is traditionally known as the ‘simple present’ tense, and is running as the ‘present continuous’. What’s odd about these labels is that the simple present tense – runs – actually can’t be used to refer to an action that’s happening at the moment of speaking. To see this, imagine that you and Jane are in a room. You are speaking on the phone to Michael. While you’re still talking Jane gets up, waves, and moves towards the door. You shout out ‘goodbye’ and Michael asks what’s happening. Your reply could only be (23a), and not (23b)

The ‘simple’ present is unavailable as an option for actions happening at the moment of speaking; only the present continuous can be used. That’s far from being the end of the story, however. Note that we can use the simple present to describe an action that someone habitually takes, even if they’re not performing it now. For instance, She flies is a good reply to the question ‘how does Jane get to Canberra?’ regardless of whether Jane is currently in the air. As long as flying is her regular mode of transport the simple present tense is appropriate.
Both varieties of the present can be used to describe future events:

QUESTION Can you discern any regular semantic difference between the simple present and the continuous on the basis of this reply?
And it even works the other way round: there are situations where the future tense can be used to refer to a situation unfolding at the present moment. For example, (25) often has present time reference:

The speaker who says this doesn’t mean to imply that they’re not already looking forward to it now. Instead, the future will look forward seems equivalent in its temporal reference to the present continuous, I’m looking forward: both refer to the present time.
The future tense, then, can sometimes be used to refer to presently occurring actions. To make matters worse, we can sometimes use the present tense to refer to past actions. This is especially common in narrative:

The events being related occurred in the past, but the speaker chooses the present tense to refer to them.
Clearly, there is a lot more to the use of the ‘past’, ‘present’ and ‘future’ tenses in English than those simple labels imply. We will return to the description of English at the end of this section.