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" [1] The first premise is that you should know that in the world as a whole and in its parts, both upper and earthly, there is nothing which forms an exception to the facts that God is the cause of its being and origination and that God has knowledge of it, controls it, and wills its existence; it is all subject to His control, determination, knowledge, and will. This is a general and superficial account, although in these assertions we intend to describe it truly, not as the theologians understand it; and it is possible to produce proofs and demonstrations of that. Thus, if it were not that this world is composed of elements which give rise to good and evil things in it and produce both righteousness and wickedness in its inhabitants , there would have been no completion of an order for the world. For if the world had contained nothing but pure righteousness, it would not have been this world, but another one, and it would necessarily have had a composition different from the present composition; and likewise if it had contained nothing but sheer wickedness, it would not have been this world but another one. But whatever is composed in the present fashion and order contains both righteousness and wickedness.
[2] The second premise is that according to the ancients Rewards is the occurrence of pleasure in the soul corresponding to the extent of its perfection, while Punishment is the occurrence of pain in the soul corresponding to the extent of its deficiency. So the soul's abiding in deficiency is it's 'alienation from God the exalted', and this is the 'curse' 'the penalty', [God's] 'wrath' and 'anger', and pain comes to it from that deficiency; while its perfection is what is meant by [God's] 'satisfaction', with it, its 'closeness' and 'nearness' and 'attachment'. This, then, and nothing else is the meaning of 'Reward' and 'Punishment' according to them.
[3] The third premise is that the resurrection is just the return of human souls to their own world: this is why God the Exalted has said, 'O tranquil soul, return to your Lord, satisfied and satisfactory.'
These are summary statements that need to be supported by their proper demonstrations. "
― Avicenna ,
37
" However, the four-elements concept is a different system of classification of matter than is our periodic table of elements; it is based on the physical state (solid, liquid, gas, energy), acceptance or rejection of moisture (wet, dry), acceptance or rejection of heat (hot, cold), and relationship to other elements (inner, middle, outer, mixed). Why is such a classification needed? The answer is simple: because it is compatible with the biological nature of living organisms. The physical state, heat, and water are three criteria that can describe the conditions of a biological entity—organs, structures, biochemical compounds, liquids, and such. "
― Avicenna , القانون في الطب
38
" So in a modern interpretation, the humors are not the blood components, as some have interpreted, but rather the chemical classes derived from food such as carbohydrates, proteins, lipids, organic acids, and their intermediates, which replenish the body with nutrients carried in the blood. Abnormal humors result from the incomplete breakdown of these classes of molecules in the bloodstream, or their aggregation (polymerization) and precipitation. "
― Avicenna , القانون في الطب
