In meditation instruction the following words occur frequently: ajjhattam, bahiddha, ajjhatta-bahiddha.
This corresponds to internal, external, internally and externally. The traditional outlook on this is to meditate on ones body and another's body. (The Way of Mindfulness - Soma Thera)
But some traditions interpret this as differently:
These are the Buddha’s words. Certain commentaries or subcommentaries have been written on them, some 1,000 to 1,500 years after the Buddha, and some even more recently. They give many good explanations of the Buddha’s words, and also descriptions of a whole spectrum of life and society at that time—political, social, educational, and economic aspects. However they give certain interpretations which this tradition of meditation cannot accept. For instance, here a commentary takes ajjhattaṃ as the meditator’s body—which is acceptable—but bahiddhā as the body of someone else, even though no one else is there. It explains that the meditator can simply think of someone else, and how all beings similarly breathe in and out. We cannot agree with this because this is imagination, and in this tradition vipassanā or anupassanā is to observe within your own body (kāye). Therefore for us bahiddhā is the surface of the body, but still within its framework.
Ajjhatta-bahiddhā can also be understood in relation to the five sense doors. When an outside object comes into contact with the eyes, ears, nose, tongue, or body surface, it is felt within the framework of the body, but on the surface of the body. Even the mind is within the framework of the body, although its object may be outside. The Sutta still does not intend you to start thinking of or seeing another body.
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Another tradition interprets ajjhattaṃ as the feeling on one’s own body, bahiddhā as the feeling on someone else’s body, and ajjhatta-bahiddhā as switching between the two. As before, our tradition does not accept this. The meditator is working alone, whether in the forest, under a tree, or in a cell. It is argued that when begging for food the monk encounters others and has this opportunity to feel their breath or sensations. However the eyes of serious meditators are downcast (okkhitta-cakkhu) and at most they might see someone else’s legs as they walk: so this interpretation seems illogical. Of course, at a very high stage of observation the meditator becomes very sensitive to the sensations of others also, and to the vibrations of the surrounding atmosphere and of animate and inanimate objects. Possibly it could be understood in this way.
(Source: Discourses on Satipatthana Sutta - S. N. Goenka)
