Suppose we are looking at a red wooden chair. Here is red something we bring in as light just gets absorbed and reflected, which we here perceive as red. Despite this behaviour, of absorbing and reflecting, is what we perceive the way we express it (AN 6.63). Wooden chair is also something which we bring in as wood has no notion of being intended to sit on; it just behaves as wood does. And as it is our experience, it is personal. It may not feel that way as perceptions are similar between species, and we can communicate about them which gives the impression of them being public. But it are just the aspects (behaviour) of form that are public and which found footing in our experience when picked up; which then became this "coloured form". Both, and the behaviour of form and the form picked up are called form (SN 12.2). Form consists of a mix of four primary behaviours, the great essences (mahābhūtā):
Earthiness (pathavī). Pathavī, says the dictionary, is expansion. It is used as earth, or earthiness if we talk about the behaviour; earth is from the earthiness. The behaviour of earth is that it takes up space. Like the planet, which is largely covered with water (udaka).
Fluidity (āpo). The behaviour of fluidity we can see with water (udaka) as ice, liquid water, vapour. And thus also accounts for certain surfaces which have a role in absorbing and reflecting light.
Heat (tejo). The behaviour of heat is that it allows for change. AN 5.197 shows that this aspect can disturb upper in the air (ākāsa) by which arisen clouds go away. So the weather changes, temperature change (the change is felt as warm, hot), ice can melt, liquids can vaporize, it can deform.
Turbulence (vāyo). Vāyo relates to wind (vāto). And the behaviour of wind (vāto) is that it blows (vāti, vāyati). It is the movement, motion. Related to wind I call it turbulence.
The primary behaviours we thus see in earth (pathavī), water (udaka), fire (aggi) and wind (vāto), as each carries its distinguishing aspects more prominent. Apart from these, outer ones, there are also the inner ones as the body is of the four essences. Thus we see them more prominently represented f.i. as the earthiness in bones, heat in body heat, the fluidity in blood and turbulence as the winds in the belly.
The point is that these essences follow their own agenda, no matter how we would like them to be, no matter how we perceive them to be. All the changes we can make to them are already granted by them; it is already within their domain. The internal earth aspect, the aspect of earthiness, and the external earth aspect are just the earth aspect. Earth is earth through and through, idem for the others. And as their behaviour is always in accordance to their own domain they should not be seen as me, mine, myself, etc. But while the body isn't ours, the actions (kammā) with it are (SN 3.20).
Pāḷi-English
Mahābhūta great essence.
Pathavī (f.) earth, earthiness.
Āpo (nt.) fluidity.
Tejo (nt.) heat.
Vāyo (nt.) turbulence.