All the first turning of the wheel of dharma are teachings on exploring, "Why do we suffer?", and, "What is the root of suffering?", and, "What is the root of happiness?" That's why I stressed that the main quality of the Foundation Yana is curiosity and inquisitiveness it's really looking. Without this, nothing ever becomes personal experience.
In these first turning teachings, the Foundation teachings, the Buddha taught on groundlessness, as I've already expressed. The Buddha always taught on groundlessness. It's probably what distinguishes Buddhism from other world religions because certainly compassion doesn't distinguish Buddhism, and a lot of things are in common. But the teaching on groundlessness sometimes called emptiness, or openness, or this word shunyata is so much the earmark of Buddhism. The Buddha always taught it.
In the first turning teachings, he taught it in the form of impermanence, as I said, everything is always shifting, moving; it's not static, it's dynamic. And he taught it in terms of egolessness, that this self is also shifting, moving, it's not a fixed identity that "we're like this" or that "you are like this" neither self nor other, subject nor object are fixed.
Something that we're actually not going to get into talking about in this course, but a lot of teachings in the first turning are teachings about interdependence, which is that self and other, subject and object, one does not exist without the other everything is all of one piece. All of that is teaching on groundlessness. It's like there's nothing to hold on to.
If you're really interested in this, you can study the Abhidharma, which goes into it in great detail. There are a great deal of teachings on the skandhas, for instance, and then some other things that are also referred to in the Heart Sutra, such as the dathus and the nidanic chain of cause and effect and the Four Noble Truths. All these things he taught in great detail, about really looking into the cause of suffering as being this inability to relax with the truth of groundlessness.
He always taught this, and he taught it in terms of very clear explanations, such as the development of ego (Trungpa Rinpoche's chapter on the monkey in the house) and the skandhas you think there's something there, but actually, when you look into it, everything is moving, shifting, dynamic, in terms of self and other, and form, feeling, perception, concept, and consciousness (thoughts and emotions), so he taught about the skandhas. So, groundlessness was already taught.