"The most reckless and treacherous of all theorists is he who professes to let facts and figures speak for themselves." (Alfred Marshall, "The Present Position of Economics", 1885)
"Again, most of the chief distinctions marked by economic terms are differences not of kind but of degree. At first sight they appear to be differences of kind, and to have sharp outlines which can be clearly marked out; but a more careful study has shown that there is no real breach of continuity. It is a remarkable fact that the progress of economics has discovered hardly any new real differences in kind, while it is continually resolving apparent differences in kind into differences in degree. We shall meet with many instances of the evil that may be done by attempting to draw broad, hard and fast lines of division, and to formulate definite propositions with regard to differences between things which nature has not separated by any such lines." (Alfred Marshall, "Principles of Economics", 1890)
"And as the number of combinations that can be made on the chess-board, is so great that probably no two games exactly alike were ever played; so no two games which the student plays with nature to wrest from her hidden truths, which were worth playing at all, ever made use of quite the same methods in quite the same way." (Alfred Marshall, "Principles of Economics", 1890)
"But a training in mathematics is helpful by giving command over a marvellously terse and exact language for expressing clearly some general relations and some short processes of economic reasoning; which can indeed be expressed in ordinary language, but not with equal sharpness of outline. And, what is of far greater importance, experience in handling physical problems by mathematical methods gives a grasp, that cannot be obtained equally well in any other way, of the mutual interaction of economic changes. The direct application of mathematical reasoning to the discovery of economic truths has recently rendered great services in the hands of master mathematicians to the study of statistical averages and probabilities and in measuring the degree of consilience between correlated statistical tables." (Alfred Marshall, "Principles of Economics", 1890)
"Economic laws are statements with regard to the tendencies of man's action under certain conditions. They are hypothetical only in the same sense as are the laws of the physical sciences: for those laws also contain or imply conditions. But there is more difficulty in making the conditions clear, and more danger in any failure to do so, in economics than in physics. The laws of human action are not indeed as simple, as definite or as clearly ascertainable as the law of gravitation; but many of them may rank with the laws of those natural sciences which deal with complex subject-matter." (Alfred Marshall, "Principles of Economics", 1890)
"Economic science is but the working of common sense aided by appliances of organized analysis and general reasoning, which facilitate the task of collecting, arranging, and drawing inferences from particular facts. Though its scope is always limited, though its work without the aid of common sense is vain, yet it enables common sense to go further in difficult problems than would otherwise be possible." (Alfred Marshall, "Principles of Economics", 1890)
"In common use almost every word has many shades of meaning, and therefore needs to be interpreted by the context." (Alfred Marshall, "Principles of Economics", 1890)
"In physical sciences indeed, whenever it is seen that a group of things have a certain set of qualities in common, and will often be spoken of together, they are formed into a class with a special name; and as soon as a new notion emerges, a new technical term is invented to represent it. But economics cannot venture to follow this example. Its reasonings must be expressed in language that is intelligible to the general public; it must therefore endeavour to conform itself to the familiar terms of everyday life, and so far as possible must use them as they are commonly used." (Alfred Marshall, "Principles of Economics", 1890)
"It is sometimes said that the laws of economics are 'hypothetical'. Of course, like every other science, it undertakes to study the effects which will be produced by certain causes, not absolutely, but subject to the condition that other things are equal, and that the causes are able to work out their effects undisturbed. Almost every scientific doctrine, when carefully and formally stated, will be found to contain some proviso to the effect that other things are equal: the action of the causes in question is supposed to be isolated; certain effects are attributed to them, but only on the hypothesis that no cause is permitted to enter except those distinctly allowed for. It is true however that the condition that time must be allowed for causes to produce their effects is a source of great difficulty in economics." (Alfred Marshall, "Principles of Economics", 1890)
"Natura non facit saltum."
"Nature does not undergo discontinuities." (Alfred Marshall, "Principles of Economics", [motto] 1890)
"Nature's action is complex: and nothing is gained in the long run by pretending that it is simple, and trying to describe it in a series of elementary propositions." (Alfred Marshall, "Principles of Economics", 1890)
"No doubt statistics can be easily misinterpreted; and are often very misleading when first applied to new problems. But many of the worst fallacies involved in the misapplications of statistics are definite and can be definitely exposed, till at last no one ventures to repeat them even when addressing an uninstructed audience: and on the whole arguments which can be reduced to statistical forms, though still in a backward condition, are making more sure and more rapid advances than any others towards obtaining the general acceptance of all who have studied the subjects to which they refer." (Alfred Marshall, "Principles of Economics", 1890)
"Secondly, the growth of exact habits of thought in economics is making people more careful to state distinctly the premises on which they reason. This increased care is partly due to the application by some writers of mathematical language and mathematical habits of thought. It is indeed doubtful whether much has been gained by the use of complex mathematical formulæ. But the application of mathematical habits of thought has been of great service; for it has led people to refuse to consider a problem until they are quite sure what the problem is; and to insist on knowing what is, and what is not intended to be assumed before proceeding further." (Alfred Marshall, "Principles of Economics", 1890)
"The best grouping, therefore, for the purposes of science is that which collects together all those facts and reasonings which are similar to one another in nature: so that the study of each may throw light on its neighbour. By working thus for a long time at one set of considerations, we get gradually nearer to those fundamental unities which are called nature's laws: we trace their action first singly, and then in combination; and thus make progress slowly but surely. The practical uses of economic studies should never be out of the mind of the economist, but his special business is to study and interpret facts and to find out what are the effects of different causes acting singly and in combination." (Alfred Marshall, "Principles of Economics", 1890)
"The law of increasing return may be worded thus:—An increase of labour and capital leads generally to improved organization, which increases the efficiency of the work of labour and capital." (Alfred Marshall, "Principles of Economics", 1890)
"The most valuable of all capital is that invested in human beings." (Alfred Marshall, "Principles of Economics", 1890)
"The raison d'être of economics as a separate science is that it deals chiefly with that part of man's action which is most under the control of measurable motives; and which therefore lends itself better than any other to systematic reasoning and analysis. We cannot indeed measure motives of any kind, whether high or low, as they are in themselves: we can measure only their moving force." (Alfred Marshall, "Principles of Economics", 1890)
"The study of theory must go hand in hand with that of facts: and for dealing with most modern problems it is modern facts that are of the greatest use." (Alfred Marshall, "Principles of Economics", 1890)
"The term 'law' means then nothing more than a general proposition or statement of tendencies, more or less certain, more or less definite. Many such statements are made in every science: but we do not, indeed we can not, give to all of them a formal character and name them as laws. We must select; and the selection is directed less by purely scientific considerations than by practical convenience. If there is any general statement which we want to bring to bear so often, that the trouble of quoting it at length, when needed, is greater than that of burdening the discussion with an additional formal statement and an additional technical name, then it receives a special name, otherwise not." (Alfred Marshall, "Principles of Economics", 1890)
"To conclude provisionally: economists study the actions of individuals, but study them in relation to social rather than individual life; and therefore concern themselves but little with personal peculiarities of temper and character. They watch carefully the conduct of a whole class of people, sometimes the whole of a nation, sometimes only those living in a certain district, more often those engaged in some particular trade at some time and place: and by the aid of statistics, or in other ways, they ascertain how much money on the average the members of the particular group, they are watching, are just willing to pay as the price of a certain thing which they desire, or how much must be offered to them to induce them to undergo a certain effort or abstinence that they dislike. The measurement of motive thus obtained is not indeed perfectly accurate; for if it were, economics would rank with the most advanced of the physical sciences; and not, as it actually does, with the least advanced." (Alfred Marshall, "Principles of Economics", 1890)
"[…] facts by themselves are silent. Observation discovers nothing directly of the actions of causes, but only of sequences in time." (Alfred Marshall)
"Statistics are the straw out of which I, like every other economist, have to make the bricks." (Alfred Marshall)
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