 Let us assume the demand for grain is rising, and the supply can only result from successive investments of capital under conditions of under-productiveness in the rent-bearing soils, or by additional investment of capital, also with decreasing productivity, in soil A, or by the investment of capital in new lands of inferior quality than A. Let us take soil B as representative of the rent-bearing soils. The additional investment of capital demands an increase in the market-price above the hitherto prevailing price of production of 3 per quarter, in order to make possible the increased production upon B of one quarter (which may here stand for one million quarters, just as every acre may stand for one million acres). Increased output may also be yielded by soils C and D, etc., the soils bearing the highest rent, but only with decreasing surplus-productiveness; but it is assumed that the quarter from B is necessary in order to meet the demand. If this quarter is more cheaply produced by investing more capital in B than with the same addition of capital to A, or by descending to soil A - 1, which may, e.g., require 4 to produce a quarter, whereas the addition to capital A might do so for 3 , then the additional capital on B will regulate the market-price. A produces a quarter for 3, as heretofore. Similarly B, as before, produces a total of 3 quarters at an individual price of production of 6 for its total output. Now, if an additional 4 of production price (including profit) becomes necessary on B in order to produce an additional quarter, whereas it could have been produced on A for 3 , then it would naturally be produced on A, rather than on B. Let us assume, then, that it can be produced on B with the additional price of production of 3 . In this case, 3 would become the regulating price for the entire output. B would now sell its present output of 4 quarters for l5 . Of this 6 is the price of production for the first 3 quarters and the 3 for the last quarter, i.e., a total of 9 . This leaves a surplus-profit for rent = 6 as against the former 4 . In this case, an acre of A would also yield a rent of 1 ; but it would not be the worst soil A, but rather the better soil B that would regulate the price of production of 3 . Of course, we assume here that new soil of quality A and equally favourable location as that hitherto cultivated is not available, but that either a second investment of capital in the already cultivated plot A at a higher price of production, or the cultivation of an even poorer soil A-1, is required. As soon as differential rent II comes into force through successive investments of capital, the limits of the rising price of production may be regulated by better soil; and the worst soil, the basis of differential rent I, may also yield rent. This, even with a single differential rent, all cultivated land would yield rent. We would then have the following two tables, where by price of production we mean the sum of the invested capital plus 20% profit; in other words, on every 2 of capital of profit or a total of 3. This is the state of affairs before the new capital of 3 , which yields only one quarter, is invested in B. After this investment, the situation looks as follows: [This, again, is not quite correctly calculated. First of all, the cost of the 4 qrs for farmer B is, in the first place, 9 : in price of production and, secondly, 4 in rent, i.e., a total of 14; average per quarter = 3 . This average price of his total production thus becomes the regulating market-price. Thus, the rent on A would amount to 1/9 instead of , and that on B would remain 4 as heretofore; 4 qrs at 3 = 14 and, if we deduct 9 in price of production, 4 remain for surplus-profit. We see, then, that in spite of the required change in numerical values this illustration shows how, by means of differential rent II, better soil, already yielding rent, may regulate the price and thus transform all soil, even hitherto rentless, into rent-bearing soil. F. E.] The grain-rent must rise as soon as the regulating price of production of the grain rises, i.e., as soon as the price of production of a quarter of grain from the regulating soil, or the regulating invested capital in one of the various soil types, rises. It is the same as though all soils had become less productive and produced, e.g., only 5/7 quarter instead of 1 quarter with every new investment of 2 . Whatever else they produce in grain with the same investment of capital is transformed into surplus-product, which represents the surplus-profit and therefore the rent. Assuming the rate of profit remains the same, the farmer can buy less grain with his profit. The rate of profit may remain the same if wages do not rise either because they are depressed to the physical minimum, i.e., below the normal value of labour-power; or because the other articles of consumption needed by the labourer and supplied by manufacture have become relatively cheaper; or because the working day has become longer or more intensive, so that the rate of profit in non-agricultural lines of production, which, however, regulates the agricultural profit, has remained the same or has risen; or, finally, because more constant and less variable capital is employed in agriculture, even though the amount of capital invested is the same. We have thus considered the first method by which rent may arise on the hitherto worst soil A without taking still worse soil under cultivation; that is, rent may arise from the difference between its individual, hitherto regulating, price of production and the new, higher price of production, whereby the last additional capital employed under conditions of under-productiveness upon the better soil supplies the necessary additional produce. If the additional produce had to be supplied by soil A-1, which cannot produce a quarter for less than 4, then the rent per acre of A would have risen to 1. But, in this case, soil A-1 would have taken the place of A as the worst cultivated soil, and the latter would have moved into the lowest position in the sequence of rent-bearing soils. Differential rent I would have changed. This case, then, is not included in the consideration of differential rent II, which arises from the varying productiveness of successive investments of capital in the same piece of land. But aside from this, differential rent may arise on soil A in two other ways. With the price unchanged any given price, even a lower one compared to former ones when the additional investment of capital results in surplus-productiveness, which prima facie, and up to a certain point must always be the case precisely on the worst soil. Secondly, however, when the productiveness of successive investments of capital in soil A decreases. It is assumed in both cases that the increased production is required to meet demand. But from the point of view of differential rent, a peculiar difficulty arises here owing to the previously developed law according to which it is always the individual average price of production per quarter for the total production (or the total outlay of capital) which acts as the determining factor. In the case of soil A, however, there is not, as in the cases of the better soils, another price of production which limits for new investments of capital the equalisation of the individual with the general price of production. For the individual price of production of A is precisely the general price of production regulating the market-price. Let us assume: 1) When the productiveness of successive investments of capital is increasing, 1 acre of A will produce 3 qrs instead of 2 qrs given an investment of 5 corresponding to a price of production of 6. The first investment of 2 yielded 1 qr, the second 2 qrs. In this case, a price of production of 6 will yield 3 qrs, so that the average cost of a quarter will be 2; i.e., if the 3 qrs are sold at 2 per quarter, then A, as heretofore, does not yield any rent, but only the basis of differential rent II has been altered; the regulating price of production is now 2 instead of 3; a capital of 2 now produces an average of 1 qrs on the worst soil, instead of 1 qr, and now this is the official productivity for all better soils given an investment of 2 . From now on, a portion of their former surplus-product enters into the formation of their necessary output, just as a portion of their surplus-profit enters into forming the average profit. On the other hand, if the calculation is made upon the basis of better soils, where the average calculation does not alter the absolute surplus at all, because for them the general price of production is the limit for the investment of capital, then a quarter from the first investment of capital costs 3 and the 2 qrs from the second investment cost only 1 each. This would thereby give rise to a grain-rent of 1 qr and a money-rent of 3 on A, but the 3 qrs would be sold for the old price of 9. If a third investment of 2 were made under conditions of the same productiveness as the second investment, then the total would be 5 qrs for a price of production of 9. If the individual average price of production of A should remain the regulating price, then a quarter would now be sold at 1 4/5. The average price would have fallen once more not through a new rise in productiveness of the third investment of capital, but merely through the addition of a new investment of capital having the same additional productiveness as the second. Instead of raising the rent as on the rent-bearing soils, the successive investments of capital in soil A of higher, but constant productiveness would proportionally lower the price of production and thereby, everything else being equal, the differential rent on all other soils. On the other hand, if the first investment of capital which produces 1 qr at a price of production of 3 should in itself remain regulating, then 5 qrs would be sold for 15, and the differential rent of the later investments of capital in soil A would amount to 6. The additional capital per acre of soil A, however it is applied, would be an improvement in this case, and would make the original portion of capital more productive. It would be ridiculous to say that of the capital had produced 4 qr and the other 4 qrs. For 9 per acre would always produce 5 qrs, while 3 would produce only 1 qr. Whether or not a rent would arise here, whether or not a surplus-profit would be derived, would depend wholly upon the circumstances. Normally the regulating price of production would have to fall. This would be the case, if this improved but more expensive cultivation of soil A should occur only because it also takes place on the better soils, in other words, if a general revolution in agriculture should occur; so that when we now refer to the natural fertility of soil A, it is assumed that it is worked with 6 or 9 instead of 3. This would particularly apply if the bulk of cultivated acres of soil A, which furnish the main supply of a given country, should employ this new method. But if the improvement should at first extend only to a small area of A, then this better cultivated portion would yield a surplus-profit, which the landlord would be quick to transform wholly or in part into rent, and to fix in the form of rent. In this way if the demand kept pace with the increasing supply as more and more of soil A began to employ the new method of cultivation, rent might be gradually formed on all soil of quality A, and the surplus-productivity might be eliminated wholly or in part, depending on market conditions. The equalisation of the price of production of A to the average price of its produce obtained under conditions of increased outlay of capital might thus be prevented by fixing the surplus-profit of this increased investment of capital in the form of rent. Thus, as was previously seen to be the case for the better soils when the productiveness of the additional capital decreased, it would again be the transformation of surplus-profit into ground-rent, i.e., the intervention of property in land, which would raise the price of production, instead of the differential rent merely being the result of the difference between the individual and the general price of production. It would prevent, in the case of soil A, the coincidence of both prices because it would interfere with the regulation of the price of production by the average price of production on A; it would thus maintain a higher price of production than necessary and thereby create rent. Even if grain were freely imported from abroad, the same result could be brought about or perpetuated by compelling farmers to use soil capable of competing in grain cultivation without yielding rent, at the price of production regulated from abroad, for other purposes, e.g., pasturage, so that only rent-bearing soils would be used for grain cultivation, i.e., only soils whose individual average price of production per quarter were below that determined from abroad. On the whole, it is to be assumed that in the given case, the price of production will fall, but not to the level of its average; it will be higher than the average, but below the price of production of the worst cultivated soil A, so that the competition from new soil A is limited. 2) When the productiveness of additional capitals is decreasing. Let us assume that soil A-1 requires 4 to produce the additional quarter, whereas soil A produces it for 3 , i.e., more cheaply, but still more dearly than the quarter produced by its first investment of capital. In this case, the total price of the two quarters produced upon A would = 6 ; thus the average price per quarter = 3 3/8. The price of production would rise, but only by 3/8, whereas it would rise by another 3/8 or to 3 , if the additional capital were invested in new land which produced at 3 , and it would thus bring about a proportional increase in all other differential rents. The price of production of 3 3/8 per quarter for A would thus be equalised to its average price of production with an increased investment of capital, and would be the regulating price; thus, it would not yield any rent, since it would not produce any surplus-profit. However, if this quarter, produced by the second investment of capital, were sold for 3 , soil A would now yield a rent of , and indeed, on all acres of A in which no additional investment of capital had taken place and which thus would still produce at 3 per quarter. So long as any uncultivated fields of A remain, the price could rise only temporarily to 3 . Competition from new fields of A would hold the price of production at 3 until all land of type A, whose favourable location enables it to produce a quarter at less than 3 , would be exhausted. This is then what we would assume, although the landlord, so long as an acre of land yields rent, will not let a tenant farmer have another acre rent-free. It would again depend to what extent a second investment of capital in the available soil A had become general, whether the price of production is equalised at the average price or whether the individual price of production of the second investment of capital becomes regulating at 3 . The latter occurs only when the landowner has sufficient time until demand is satisfied to fix as rent the surplus-profit derived at the price of 3 per qr. Concerning decreasing productiveness of the soil with successive investments of capital, see Liebig. [Liebig, Die Chemie in ihrer Anwendung auf Agricultur und Physiologie, Braunschweig, 1862. Ed.] We have observed that the successive decrease in surplus-productiveness of invested capital invariably increases the rent per acre, so long as the price of production remains constant, and that this may occur even with a falling price of production. But, in general, the following is to be noted. From the standpoint of the capitalist mode of production, a relative increase in the price of products always takes place when these products cannot be secured unless an expenditure or payment not previously made is incurred. For by the replacement of capital consumed in production we mean only the replacement of values represented by certain means of production. Natural elements entering as agents into production, and which cost nothing, no matter what role they play in production, do not enter as components of capital, but as a free gift of Nature to capital, that is, as a free gift of Nature's productive power to labour, which, however, appears as the productiveness of capital, as all other productivity under the capitalist mode of production. Therefore, if such a natural power, which originally costs nothing, takes part in production, it does not enter into the determination of price, so long as the product which it helped to produce suffices to meet the demand. But if in the course of development, a larger output is demanded than that which can be supplied with the help of this natural power, i.e., if this additional output must be created without the help of this natural power, or by assisting it with human labour-power, then a new additional element enters into capital. A relatively larger investment of capital is thus required in order to secure the same output. All other circumstances remaining the same, a rise in the price of production takes place. (From a note-book "begun in mid-February 1876." [F.E.]) Differential rent and rent as mere interest on capital incorporated in the soil. The so-called permanent improvements which change the physical, and, in part, also the chemical conditions of the soil by means of operations requiring an expenditure of capital, and which may be regarded as an incorporation of capital in the soil nearly all amount to giving a particular piece of land in a certain limited locality such properties as are naturally possessed by some other piece of land elsewhere, sometimes quite near by. One piece of land is naturally level, another has to be levelled; one possesses natural drainage, another requires artificial drainage; one is endowed by Nature with a deep layer of top soil, another needs artificial deepening; one clay soil is naturally mixed with the proper amount of sand, another has to be treated to obtain this proportion; one meadow is naturally irrigated or covered with layers of silt, another requires labour to obtain this condition, or, in the language of bourgeois economics, it requires capital. It is indeed a truly amusing theory, whereby here, in the case of one piece of land whose comparative advantages have been acquired, rent is interest, whereas in the case of another piece of land which possesses these advantages naturally, it is not interest. (In fact, this is so distorted in practice that since rent really coincides in the one case with interest, it is falsely also called interest in the other cases, where this is positively not the case.) However, land yields rent after capital is invested not because capital is invested, but because the invested capital makes this land more productive than it formerly was. Assuming that all the land of a given country requires this investment of capital, every piece of land which has not received it must first pass through this stage, and the rent (interest yielded in the given case) borne by land already provided with investment of capital constitutes differential rent just as though it naturally possessed this advantage and the other land had first to acquire it artificially. This rent too, which may be resolved into interest, becomes pure differential rent as soon as the invested capital is amortised. Otherwise, one and the same capital would have to exist twice as capital. A most amusing phenomenon is that all opponents of Ricardo who oppose the idea that value determination is based exclusively on labour rather than regarding differential rent as arising from differences in soil, point out that here Nature rather than labour determines value; but at the same time they credit this determination to the location of the land, or and to an even greater extent the interest on capital put into the land during its cultivation. The same labour produces the same value in a product created during a given period of time; but the magnitude or quantum of this product, and consequently also the portion of value associated with some aliquot part of this product, depends for a given quantity of labour solely upon the quantum of product, and the latter, in turn, depends upon the productivity of the given quantum of labour rather than the absolute magnitude of this quantum. It is immaterial whether this productivity is due to Nature or to society. Only in the case when the productivity itself costs labour, and consequently capital, does it increase the price of production by a new element which Nature by itself does not do. 
Economic Manuscripts: Capital, Vol.3, Chapter 44