Aggregate as an English word means a part of a unit. So when you put aggregates together you make a unit. Take the example of our body, we have arms as one aggregate, legs as another aggregate, and so on. So, aggregates are parts of something else. When the Buddha talked about each one of us being made up of five aggregates, he was just dividing us up in a way so we could understand more fully about each part.
When we look at the body, it is fairly clear that this is part of our practice. Being mindful of our body, being mindful how we react in the body, being mindful of sensations and so on. We want to be aware of that. As far as the mind goes, it is divided into four parts. There is perception, Vedana or feelings, mental formations, and consciousness. Now consciousness is present all the time. Right now you are conscious of hearing me, so your ear consciousness is working. There are also many of you who are conscious of seeing me, so your eye consciousness is working. We are simply conscious in that moment of whatever is happening. Now the other three aggregates: perceptions, Vedana, and mental formations.
Perception is something that automatically comes every time we have a contact. Contact, let's go back to the body - the eye sees color and form, that is all that the eye does, it sees color and form, but the mind puts a perception on the color and the form. So whenever you see me you have a perception, "That is Steve." Fine. Now when you see somebody who looks like me, maybe you meet him on the boat or somewhere, you will automatically think, "Oh, that person looks like Steve." You have a perception around them.
You have perceptions on virtually everything you have a contact with, you put a label on it. Perception comes from our memory. Based on whatever we have experienced in the past we then put a perception on something we are experiencing in the present moment, even if you have never experienced a particular thing before. For example; a lot of the Thai sweets or the Thai fruits here. Most Westerners have never had many of them. So the first time you eat a Mangosteen, you look at it and what does it look like? Immediately the mind kind of thinks, "What does it look like?" You crack it open and what does it look like? Somebody may say, "It is segments inside, that is like a grapefruit or an orange." And automatically we use our memory base to try to figure out what it looks like. But quite frankly all that a Mangosteen really looks like is a Mangosteen. However, when we see something for the first time we bring our memory bank in and we try to describe what it looks like from what we have learned before.
Mental formations, this is where we do all our thinking around our contact, our perception and our Vedana. We start building stories. With that Mangosteen, we are building stories, about whether we like it, whether it is delicious, whether it has too many seeds, whether it is rotten. We build a story around the perception and the Vedana. Then we develop a whole big mental formation which can go into all of our cravings, our desires. "Oh Mangosteen, I like Mangosteen, I really love Mangosteen, oh I hope …," and we build a big story and some people can't live without Mangosteen, it gets bizarre, but that is our mental formation. It is mental formations where Mara has all of his or her power. It is in mental formations where Mara just takes over. It just invents anything. But it is also in mental formations that you have your wisdom development, your wise reflection, Yonisomanasikara. It's all a big battlefield in mental formations. Who is going to win? Get that conditioning in there, try to see things more clearly, get your wisdom going so that can beat up Mara in the scope of mental formations.