A trademark's viability depends on continued use and vigilance. When it comes to trademarks, the law has a "use it or lose it" philosophy, which makes sense in light of a trademark's role as an identifier of the source of goods and services. If there are no goods and services that are being promoted through use of the trademark, it no longer functions as one. A subsequent user can file to cancel a dormant federally registered mark, or can defend an infringement action based on abandonment.