By definition, every one of us exists in first-person present tense. Yet it's one of the most difficult tenses to write, and one in which it's very easy to make mistakes of logic. Perhaps this is because in some respects, the act of storytelling is in opposition to the act of simply being. Storytelling is invention, re-creation, the replacement of what is immediately around us with an artificial alternative. The storyteller is always a filter between us and the world, whereas true first-person present is essentially direct experience. Thus to write genuine first-person present, the author must become invisible – if you like, a filter that is entirely transparent.
This is all rather abstract, so let me give a few examples. One popular narrative tool is hindsight: the 'little did I know that disaster was looming' approach. But since first-person present puts the reader into the narrator's point of view as they experience it, it's obvious that such constructions are inappropriate. Now, it's rare for authors to overtly get this wrong (you won't find anyone writing 'little do I know that disaster is looming', or at least I hope you won't). But you will find it done in more subtle ways. Take these:
To start with, my sister and my fiancée get on OK.
For the first ten minutes, I don't move.
Both seem reasonable on the surface, yet in fact they make no logical sense. They imply knowledge of what's to come (which is impossible in first-person present); they have a hidden 'but'. To start with my sister and my fiancée get on OK … but then they begin tearing each other's hair out. For the first ten minutes I don't move … but then I leap up and dance. The point is that at the time described by the first half of each sentence, the narrator doesn't know that the situation is going to change. So constructions like this aren't genuine first-person present at all.
Fun, isn't it? But I'm just getting started. Another common logical mistake is to frame current events with an explanation that couldn't be known to the narrator at the time. The most obvious example is something like this:
After tossing and turning for a while, I drop into an uneasy dream.
Most of us don't notice when we fall asleep. Nor do we know when we're dreaming (not until we wake up again and realise with relief that we aren't being forced to resit all our school exams naked after all). This sort of thing is fine in first-person past tense, which is the narrator's retrospective view of events, and allowable in third person, which is not quite as closely limited. But a first-person present narrator shouldn't know her dream is a dream.
Another of my favourites is the impossible memory glitch, which is along the following lines:
For a moment I don't remember the terrible events of last night.
This is, quite simply, impossible. To refer to the terrible events of last night, the first-person present narrator clearly must remember them. Again, this isn't such an issue for other tenses, but the whole point of first-person present is that it describes everything exactly as it's experienced by the narrator. On a similar point, if said narrator is in an altered state of consciousness (e.g. dead drunk) then he shouldn't be able to describe events in coherent prose that gives no indication of his mental state. Logically, the narrative voice and the narrator's dialogue ought always to match in idiom and construction.
There are many other little authorial devices that act as a filter between reader and narrator, and thus remove the narrative a step from true first-person present. Something as simple as mishearing a word, for instance – if the word is written on the page correctly at the moment the narrator mishears it, that creates a mismatch between the narrator's experience and her narrative. Even certain verbs become somewhat redundant: sentences such as I remember what happened last year or I wonder why he's smiling detach the narrator from the act of remembering or wondering, and again the immediacy that is the hallmark of first-person present is lost.
Despite all this, it's worth pointing out that true first-person present narrative – stream of consciousness, or a constant description of the narrator's thoughts and experiences as they occur – would be very difficult to sustain for the course of an entire book. Not only that, it would be tiring and awkward for the reader. To create an enjoyable piece of literature, there has to be some author intervention and some imposition of structure/narrative convention. As always, there is a balance to be struck between realism and style. Nevertheless, if you are writing in first-person present, it is worth bearing the logic of the tense in mind. That way, you'll achieve as close to an authentic first-person present voice as it's possible to achieve within the constraints of a coherent novel.