Third, although there are many ways in which international cooperation can take place within narrow fields, there are also many linkages, natural and constructed, between different narrow fields. Natural linkages are the types of issues that we generally consider under the heading "fragmentation" where a rule in a particular area has effects on the achievement of policy goals in another areas. Natural linkages grow as more areas of international law are developed in greater depth, and these natural linkages are already pervasive. As the volume of international law grow, more natural linkages arise, precipitating the need to determine hoe different areas of law relate to one another. Constructed linkages may be devised in order to induce agreements that might not otherwise occur.