Refinements and Qualifications

So much for the rough outline — it has been argued in recent years [Cartwright, 1983] that the way laws of nature are related to the world is not as simple descriptions of independent matters of fact. Newton's Laws of Motion are a useful peg on to which to hang these refinements before I turn to examine the status of general statements in chemistry. Consider the First Law: ‘Every body continues in its state of rest or uniform motion unless acted upon by an impressed force’. Pure inertial motion never occurs in the material world. Is the law an idealised, cleaned up version of a cluster of similar but messy empirical generalizations? Such was once the standard view. However, the rise of the interpretation of the work of science as various kinds of model making suggest a different interpretation. Consonant with the modelling trend laws of nature are best seen as prescriptions of phenomena in model worlds. Hence they cannot fail to be correct descriptions of those phenomena. A law relates to actual observable processes via the intermediary of an iconic model, which resembles in some degree that which it models. Laws can then be given a ‘second reading’ so to say as rules for the construction of models. It is now no surprise that laws fit the models they ‘describe’ with a remarkable degree of perfection. They were the principles according to which the models were constructed in the first place. Interesting questions arise when the material for constructing iconic models runs out, as it seems to do in quantum mechanics. These questions as to the content of law-like statements in chemistry, particularly concerning bonding, will surface later in this discussion.This leads to the general question of the role of content in shaping the ‘grammar’ of scientific laws. The laws of chemistry do not generally refer to patterns of events but to transformations of substances. The fact that both event sequences and substance transformations are laid out along a time-line may make these processes look more alike than they are. The equations in which chemical knowledge is recorded describe regularities between initial and final states of material systems rather than sequential patterns of events. In the course of a chemical reaction the constituents of the original substances are re-arranged to become different substances in the final state towards which the system tends. Chemical equations do not describe sequences of events.Though the last thousand years has seen the coming and going of several ideas as to what the constituents of material stuffs might be, the outline metaphysics is more or less the same. The four Greek elements, Hot, Cold, Wet and Dry, the proportions of which determined the observable properties of all things, including people, were still important in the renaissance. Other elements were proposed, such as mercury, sulphur and salt. However, chemical changes, transformations of substances, were thought of in much the same way as they are now, that is as substantial changes that come about by the rearrangements of constituent elements, whatever those elements may be.The metaphysics of all these schemes, including our own, is based on the principle that compounds do not display the observable characteristics of the elements of which they composed. Compounds generally display emergent properties. Neither carbon, hydrogen nor oxygen is sweet, though C₁₂H₂₂O₁₁ is. As Joseph Earley [2005, 85-102] has argued so persuasively, there is no salt in the sea!There is a further distinction between chemical equations and laws of physics, to do with the meaning of the notations. In physics, for the most part, ‘+’ and ‘=’ are to be read numerically. In chemistry the very same sign forms mean something quite different. ‘+’ means something like ‘reacting’, while ‘=’ means ‘gives rise to’ or something like that. Of course, as Benjamin Brodie pointed out, every chemical equation is accompanied by a ghostly sibling, in which the atomic weights of the elements are inserted. Then the meanings of the notation change radically. Juxtaposing letters in a chemical formula means ‘combined with’. Juxtaposing letters in the gravimetric equation means ‘add’.

Date: 2015-01-12; view: 1422