"These six main objects (sounds, colors, smells, tastes, touches, and mental objects) are all that we can know. No matter how wildly adventurous our lives are, we still can't experience anything other than these half-dozen forms. Since mind and object are the only building blocks from which a moment of life can be fashioned, there is nothing else that could possibly take place in the now. "

What's so great about now? - Tricycle:  The Buddhist Review - Winter 2006