quality of rate and state in the inorganic realm. Lyell According to Reijer Hooykaas (1963), Lyell's uniformitarianism is a family of four related propositions, not a single idea: Uniformity of law – the laws of nature are constant across time and space. Uniformity of methodology – the appropriate hypotheses for explaining the geological past are those with analogy today. Uniformity of kind – past and present causes are all of the same kind, have the same energy, and produce the same effects. Uniformity of degree – geological circumstances have remained the same over time. None of these connotations requires another, and they are not all equally inferred by uniformitarians. Gould explained Lyell's propositions in Time's Arrow, Time's Cycle (1987), stating that Lyell conflated two different types of propositions: a pair of methodological assumptions with a pair of substantive hypotheses. The four together make up Lyell's uniformitarianism. Methodological assumptions The two methodological assumptions below are accepted to be true by the majority of scientists and geologists. Gould claims that these philosophical propositions must be assumed before you can proceed as a scientist doing science. "You cannot go to a rocky outcrop and observe either the constancy of nature's laws or the working of unknown processes. It works the other way around." You first assume these propositions and "then you go to the outcrop." Uniformity of law across time and space: Natural laws are constant across space and time. The axiom of uniformity of law <ref name=gould1987>, "Making inferences about the past is wrapped up in the difference between studying the observable and the unobservable. In the observable, erroneous beliefs can be proven wrong and be inductively corrected by other observations. This is Popper's principle of falsifiability. However, past processes are not observable by their very nature. Therefore, the invariance of nature's laws must be assumed to come to conclusions about the past."</ref> is necessary in order for scientists to extrapolate (by inductive inference) into the unobservable past. The constancy of natural laws must be assumed in the study of the past; else we cannot meaningfully study it. Uniformity of process across time and space: Natural processes are constant across time and space. Though similar to uniformity of law, this second a priori assumption, shared by the vast majority of scientists, deals with geological causes, not physicochemical laws. The past is to be explained by processes acting currently in time and space