From the extermophile Archeabacteria residing on volcanic rims to humans cozy in their homes and everything in between; there is not a single place on Earth barren of life. Whether visible or requiring heavy microscopic machinery, the world is filled with life. Due to the extreme variety of life, a problem arises in finding a linking factor which can be used to form a definition that properly picks out all that is meant by the word life. The current definition of life is a chemical structure that resists entropy and can participate in darwinian evolution. It is important that there is a consistent and functional definition of the life because there must be a way to determine when something is no longer alive. This would be useful both on our own planet in determining when something can de considered alive or dead, and in our exploration of the universe. It has proved difficult to define life on other planets and an adequate definition is needed to do so. Through defining an adequate theoretical definition and expressing the problems that arise and the conditions required, the difficulties of defining life will be explored. .
In order to identify or classify anything, there must first be an adequate definition established. To fulfill this, a definition must reveal the essence of what it is defining so that it can be determined from what it is not. The definition does this by providing necessary and sufficient conditions for being such a defined thing. A necessary condition would be that the defined must be in the extension of what is being defined. The extension is the actual objects in the world that are being referenced to by the connotation of the definition. For example, the one-cent coin accepted as U.S. currency is in the extension of the connotation penny. A sufficient condition for being the defined thing is a set of features such that if A has feature Y, then A is in the extension of the defined.
