Four dimensions of mindfulness
In Buddhism, there are several terms that are translated as mindfulness or are closely related to the concept of mindfulness, and each of them has a different flavor. It's useful to get to know the different dimensions of mindfulness.
Sati most simply means "recollection", both in the sense of memory and in the sense of "having gathered together once more". Sati is the aspect of mindfulness that knows what is going on at any particular time. For example, when we're aware of our posture, and that we're in a certain mood, and that our mind is alert or dull, then this is sati.
Sati is knowing what is going on, and we need to know this in order to be able to make any meaningful changes. If you don't know where you are, how can you get to where you want to go?
Sampaja˝˝a is the aspect of mindfulness that extends over a period of time. It includes an awareness of purpose (where we want to go), and an awareness of where we've already been. Often in Buddhist texts, the terms sati and sampaja˝˝a are joined together into one compound term, sati-sampaja˝˝a, and it's this compound term that's often translated as "mindfulness". Sampaja˝˝a is necessary so that we can periodically compare where we are going with where we want to be. Sampaja˝˝a is like the compass that gives us our bearings.
Dhamma-vicaya is the aspect of mindfulness that categorizes our experience in terms of some model or another. In the second Wildmind book we'll be learning about ways to categorize our distractions (the hindrances) as well as positive qualities that we can develop in meditation (the dhyana factors). Dhamma-vicaya is the act of comparing our inner experience to a mental map, so that we can navigate more effectively towards our goal.
The simplest kind of map you can have is something like a division of your emotional states into "positive" (those states that are constructive and helpful, like love, empathy, confidence) and "negative" (those that tend to be destructive, like hatred, addictive craving, cynicism).
Appamada is mindfulness in the sense of watchfulness or vigilance. It's mindfulness imbued with a sense of the importance of the task in hand. Some texts say that if you lose your mindfulness you should grab it up again like a soldier in the heat of battle who has dropped his sword. Another interesting analogy is that we should act as swiftly as someone who has discovered that his or her hat is on fire. Appamada is the dynamic aspect of mindfulness.
All of these aspects of mindfulness work together synergistically. To some extent we may have to develop them separately, but in order to develop one fully we have to develop the others.