Kanuni ya pili muhimu ya ubepari ni kanuni inayobainisha thamani ya bidhaa. Thamani ya bidhaa ni kiwango cha umuhimu wake, kwa kulinganishwa na mtu fulani au kwa kulinganishwa na kitu kingine. Thamani inapotumiwa kwa kulinganishwa na mtu, huitwa "thamani ya manufaa," au kwa urahisi "manufaa." Inapopimwa kwa kulinganishwa na kitu kingine, huitwa "thamani ya kubadilishana" au kwa urahisi "thamani." Chini ya ubepari, thamani ya manufaa ya kitu hupimwa kwa manufaa yake ya pembezoni. Manufaa ya pembezoni ya kitengo ni ule manufaa unaotosheleza hitaji dhaifu zaidi. Hii inajulikana kama nadharia ya "kupungua kwa matumizi ya pembezoni"38. Kulingana na nadharia hii, manufaa hayapimwi kwa mtazamo wa mzalishaji na gharama za uzalishaji peke yake; jambo hilo lingezingatia ugavi lakini si mahitaji. Wala hayapimwi kwa mtazamo wa mlaji peke yake (manufaa, kutamanika, na upatikanaji au uhaba wa jamaa); jambo hilo lingemaanisha kuzingatia mahitaji bila ugavi. Thamani ya manufaa inapaswa kuchunguzwa na kupimwa kwa mtazamo wa ugavi na mahitaji kwa pamoja.

The second major principle of capitalism is the principle which defines the value of the product. The value of the product is the degree of its importance, relative to a particular person or relative to another thing. When the value is used relative to a person, it is called “the value of the benefit,” or simply the “benefit.” When measured against another thing, it is called the “value of exchange” or simply the “value.” Under capitalism, the value of the benefit of a thing is evaluated by its marginal benefit. The marginal benefit of a unit is that benefit which satisfies the weakest need. This is known as “the diminishing marginal utility” theory38. According to this theory, the benefit is not evaluated from the viewpoint of the producer and the costs of production only; this would only consider supply but not demand. Nor is it evaluated from the viewpoint of the consumer alone (benefit, desirability, and relative availability or shortage); this would imply the consideration of demand without supply. The benefit value should be observed and evaluated from the viewpoint of both supply and demand.

Ukomo wa kiasi cha faida (marginal utility) unasema kwamba faida ya kitu inapaswa kupimwa katika kiwango cha chini kabisa au kiwango cha chini cha kuridhika. Kwa mfano, thamani ya mkate mmoja inapaswa kupimwa katika kiwango cha chini cha njaa, na haipaswi kupimwa wakati kila mtu ana njaa au wakati anayehitaji mkate ana njaa kali sana. Kwa maneno mengine, thamani ya faida ya mkate hupimwa wakati mkate ni mwingi sokoni, si wakati kuna uhaba wa mkate. Sheria ya kupungua kwa ukomo wa kiasi cha faida (law of diminishing marginal utility) haishikiki kila wakati, kama tutakavyoona baadaye; hili huenda likawa mojawapo ya vyanzo vya kasoro na mapungufu yaliyofichika katika msingi wa ubepari.

Marginal utility states that the benefit of a thing should be assessed at the least or minimum point of satisfaction. For example, the value of a loaf of bread should be assessed at the least point of hunger and should not be assessed when everybody is hungry or when the one who needs the bread is too hungry. In other words, the benefit value of the bread is measured at a time when bread is abundant in the market, not at a time when there is a shortage of bread. The law of diminishing marginal utility does not always hold as we shall see later; this could very well be one of the sources of defects and dormant faults in the foundation of capitalism.

Thamani ya kubadilishana ni sifa inayofanya kitu kiwe kinafaa kubadilishwa na bidhaa nyingine. Nguvu ya kubadilishana kwa kitu hupimwa kwa kulinganisha na kitu kingine. Kwa mfano, thamani ya kubadilishana ya ngano kwa mahindi hukadiriwa kwa idadi ya vipimo vya mahindi vinavyopaswa kutolewa ili kupata kipimo kimoja cha ngano.

The exchange value is an attribute which makes a thing suitable for exchange with other products. The strength of exchange of a thing is measured relative to another thing. For example, the value of exchange of wheat relative to corn is estimated by the number of units of corn which should be conceded to obtain one unit of wheat.

Mabadilishano hufanyika kati ya bidhaa mbili au huduma mbili ambazo zinafanana au thamani zake ziko karibu. Kujifunza thamani ya kubadilishana ni jambo la lazima kwa wachumi kwa sababu ndiyo msingi wa kubadilishana kwa bidhaa. Ni manufaa yanayoweza kupimwa; pia hutumika kama kipimo ambacho kwacho bidhaa na huduma hupimwa, na ambacho kwacho tija ya vitendo inaweza kupimwa.

Exchange occurs between two commodities or services which are similar or close in their values. The study of the exchange value is necessary for economists because it is the basis for the exchange of products. It is a utility which can be measured; it also serves as a scale with which commodities and services are measured and by which the productivity of actions can be measured.

Uzalishaji unafafanuliwa kama kazi inayowekezwa ili kuunda manufaa au kuongeza manufaa katika kitu fulani. Ili kutambua kama kazi fulani ni yenye tija au la, au ili kubaini ni kazi ipi ina tija kubwa zaidi, lazima kuwepo na kipimo sahihi ambacho kwacho tija inaweza kupimwa. Kipimo hiki ni thamani ya kijamii ya bidhaa na huduma mbalimbali. Kwa maneno mengine, ni tathmini ya pamoja ya kazi iliyotumika na huduma iliyotolewa. Tathmini kama hii ni ya lazima kwa sababu katika zama za sasa, uzalishaji kwa lengo la kubadilishana umetawala na karibu umechukua nafasi ya uzalishaji kwa ajili ya matumizi binafsi. Katika uchumi wa leo, karibu kila mtu anabadilishana uzalishaji wake na uzalishaji wa watu wengine. Njia sahihi ya kubadilishana bidhaa na huduma ni kupitia malipo ya fidia. Ili kukadiria kiasi cha fidia kwa bidhaa au huduma, thamani ya kubadilishana inahitaji kukadiriwa. Kwa hiyo, ujuzi na ufafanuzi wa "thamani" ni kipengele muhimu katika uzalishaji na matumizi; ni muhimu kwa tafiti zote zinazolenga kukidhi mahitaji.

Production is defined as the work invested for creating benefit or increasing benefit in a thing. In order to identify whether a work is productive or not or to determine which work has greater productivity, there must be an accurate scale by which productivity can be measured. This scale is the societal value of the various products and services. In other words, it is the collective evaluation of the work spent and the service provided. Such an evaluation is necessary because in the modern time, production for the purpose of exchange has dominated and almost replaced production for consumption. In today’s economy, virtually every person exchanges his/her production with other people’s production. The proper way of exchanging products and services is through compensation. In order to estimate the amount of compensation for a product or service, the value of exchange needs to be estimated. Hence, the knowledge and definition of the “value” is an essential factor in production and consumption; it is essential for all the studies leading to the satisfaction of the needs.

Katika historia ya kisasa, thamani hii ya kubadilishana imetawaliwa na aina moja ya ubadilishanaji, yaani ubadilishanaji wa bidhaa au huduma kwa fedha. Thamani ya kubadilishana ya bidhaa au huduma kwa fedha huitwa "bei." Bei, kwa hiyo, ni kiasi cha ubadilishanaji wa bidhaa au huduma kulingana na fedha. Tofauti kati ya thamani ya kubadilishana na bei ni kwamba thamani ya kubadilishana ni uwiano wa ubadilishanaji wa kitu kimoja kuhusiana na kitu kingine chochote, wakati bei ni uwiano wa ubadilishanaji wa kitu kimoja kuhusiana na fedha. Inawezekana kwa bei za bidhaa zote kupanda au kushuka kwa wakati mmoja. Hata hivyo, haiwezekani kwa thamani za kubadilishana za bidhaa zote kulinganishwa na kila moja kupanda au kushuka kwa wakati mmoja. Pia inawezekana bei za bidhaa kubadilika bila kusababisha mabadiliko katika thamani yao ya kubadilishana au thamani yao ya manufaa. Bei ya bidhaa ni thamani moja tu kati ya thamani zake; ni thamani ya bidhaa kuhusiana na fedha. Kwa kawaida, bei imekuwa kipimo cha kweli cha kuamua kama kitu ni chenye manufaa au la, na cha kubainisha kiwango cha manufaa ya kitu hicho. Bidhaa au huduma inachukuliwa kuwa yenye tija au manufaa ikiwa jamii inaweka bei kubwa kwa bidhaa au huduma hiyo. Kiwango cha manufaa ya bidhaa au huduma hiyo hupimwa kwa bei ambayo wateja wengi wanakubali kulipa ili kuimiliki au kuitumia. Bidhaa na huduma zinazopimwa kwa bei zinaweza kuwa bidhaa au huduma yoyote: bidhaa ya kilimo au ya viwanda; huduma ya mfanyabiashara au kampuni ya usafirishaji, daktari au mhandisi.

In modern history, this value of exchange has been dominated by one type of exchange, the exchange of a product or service for money. The exchange value of a commodity or a service for money is called the “price.” The price, therefore, is the amount of exchange of a commodity or a service relative to money. The difference between the value of exchange and the price is that the value of exchange is the exchange ratio of one thing related to (any) other thing, while the price is the exchange ratio of one thing related to money. It is perceivable that the prices of all goods rise or fall at the same time. It is impossible, however, for the exchange values of all commodities relative to each other to rise or fall at the same time. It is also possible for the prices of commodities to change without resulting in a change in their value of exchange or value of benefit. The price of a commodity is only one of its values; it is the value of a commodity relative to money. Naturally, the price has become the de facto scale for deciding whether a thing is beneficial or not and for defining the degree of benefit of that thing. The commodity or the service is considered productive or beneficial if the society puts a high price for this commodity or service. The degree of benefit of this commodity or service is measured by the price which the majority of the consumers agree to pay for possessing or utilizing it. Products and services evaluated by a price can be any commodity or service: agricultural or industrial product; the service is that of a trader or transportation company, doctor or engineer.

Thamani ya bidhaa chini ya ubepari ni ya kiulinganishi (ya kidhahania) na si ya kudumu. Kwa mfano, thamani ya mkate mmoja ni faida yake ya pembezoni, ikidhani kwamba mkate huo umejaa sokoni; hili linatokana na dhana ya upungufu wa matumizi ya pembezoni. Mkate huo unapotolewa kwa mtu mwenye njaa wakati mkate ni adimu, thamani yake huwa juu mno. Thamani hiyo hupungua hadi inapotulia, pale watu wanaotaka mkate hawana tena njaa na kuna mkate wa kutosha kwa wale wanaotaka kuununua. Hivyo, thamani (ambayo ni faida ya bidhaa) inapaswa kukadiriwa wakati ambapo mahitaji ya bidhaa ni madogo kabisa na ugavi wa bidhaa ni mwingi.

he value of a commodity under capitalism is a relative (virtual) one and not absolute. The value of a loaf of bread, for example, is its marginal benefit assuming that the bread is abundant in the market; this is based on the diminishing marginal utility concept. When the loaf of bread is offered to one who is hungry and the bread is scarce, the value of the bread is too high. The value diminishes until it settles down when the people demanding the bread are no longer hungry and there is enough bread for those who want to acquire it. So the value (which is the benefit of the product) needs to be estimated at the time when the demand for the product is the lowest and the supply of the product is plentiful.

Bidhaa pia ina thamani nyingine, nayo ni thamani ya kubadilishana. Thamani ya kubadilishana ni kiasi cha bidhaa na juhudi ambazo zingeweza kubadilishwa kwa ajili ya mkate huo. Thamani hiyo inakuwa bei iwapo kile kinachopatikana kwa ajili ya mkate huo ni fedha. Thamani hizi mbili, chini ya ubepari, zimetengana, na zina majina mawili tofauti: manufaa, na thamani ya kubadilishana au fedha.

The product also has another value, which is the exchange value. The exchange value is the quantity of commodities and efforts that could be exchanged in return for the loaf of the bread. The value becomes a price if what is obtained for the loaf of the bread is money. These two values, under capitalism, are separate, and have two distinct names, benefit and the value of exchange or money.

Ufafanuzi huu wa thamani si sahihi. Zingatia kwamba katika mitazamo yote miwili ya thamani (manufaa na bei), mpima anapima thamani kulingana na mtumiaji. Mtazamo huu hautoi kipimo chochote cha manufaa ya bidhaa yenyewe. Katika kesi ya mkate, ufafanuzi wa thamani haurejelei manufaa yaliyomo ndani ya mkate kwa maana kwamba mkate una sifa ya kuondoa njaa. Kwa kweli, thamani ya mkate ni kiasi cha manufaa yaliyomo ndani yake. Kiasi hiki kinapopimwa, kipengele cha uhaba kinapaswa kuzingatiwa, lakini hakipaswi kufafanua thamani. Mtazamo huu wa thamani (kiasi cha manufaa kilichomo katika bidhaa) unashikilia iwe bidhaa imepatikana kwa uwindaji, utengenezaji, kilimo, uuzaji, au ununuzi. Manufaa yanabaki yaleyale iwe yanahusiana na mtu au yanahusiana na kitu kingine, iwe bidhaa ipo kwa wingi au ni adimu. Kwa hakika, thamani ni jina la kitu maalum chenye uhalisia maalum; si jina la kitu cha kulinganisha, kinachobadilika kwa muda na kutoka hali moja hadi nyingine. Kwa maneno mengine, thamani inapaswa kuwa kipimo cha lengo cha manufaa na si cha kulinganisha.