Under the ownership and usufruct Most economists classify assets according to their property in two groups: individual and private property or common or collective goods. However, in practice, economic studies have focused on a particular aspect of this second category: the state (also called “public good”, possibly due to influence of public domain legal concept ). This approach can be traced to Friedrich von Wieser, who states: “Apart from private finances are several” communal economy “(” Gemeinwirthschasften “in the original.” Op cit, p 209 :)…Confine my inquiries to the most important of the “communal economy” (gemeinwirthshaft), that the State. ” However, there is some confusion about that, especially with regard to terminology, apparently a result of an error in the popularization von Wieser’s vision by some of his disciples. Now the classification is not generally used in economic studies (as opposed to political economy) due to a variety of reasons -mainly because it is too general (which gives rise to some confusion and difficulties ) since it does not take into account certain aspects, for example, utlizacion and enjoyment of property-result systems have been introduced more extensive and / or complex. For example Paul A.Samuelson suggested that the commonality or otherwise of consumption is the determinant of the difference between private and public property, arguing that the latter are those “goods which all enjoy in common in that individual consumption is not so good leads to decreased consumption of such property by any other individual. ” (this came to be called “rivalry”). Subsequently Musgrave argue that the feature that really separates public from private property is the ability to exclude some of their consumption. (this is called “excludibilidad”). From these observations, modern economists generally categorize the goods from the standpoint of use in four broad groups based on these two characteristics: rivalry and excludibilidad. 1: private property, those with both rivalry as excludibilidad.(not to be confused with either goods produced or privately owned, although many are: a private consumption good, no matter who the owner or producer, someone once you use it, its availability to others decreases or Missing: irrelevant who owns the orchard, once you eat one apple this is “consumed” and the amount of apples available decreases.) 2: Natural Monopolies or of public undertakings or Pay per use: but those who have not excludibilidad rivalry (see, for example, Toll) .- 3: Public goods and pure public goods: those who possess neither or rivalry excludibilidad (air, rainwater, knowledge, etc) .- 4: Resources common-Gregory Mankiw, Elinor Ostrom, Perreira, etc – or common good: those who possess but excludibilidad rivalry. (following the example of Mankiw: fish in the ocean, environment, etc.) An alternative classification is proposed by James M.Buchanan, for whom the “pure public goods” are those without excludibilidad. All other commons are real club.: those that meet the needs of users freely at the time of use, but they involve cost sharing. It should be noted that these classifications are not completely consistent and free from defects and, consequently, may cause some confusion. For example, a common resource, although their benefit is free to a community, not necessarily community property. For example, radio signals as excludibilidad lack both rivalry. However, the property system of the issuing companies can be both private and state or community.