The modern theory now commonly applied, is the work of Swedish scientist Carolus Linnaeus (1707-1778) who had worked it out, more than two hundred years ago. He used seven major categories in his classification. Out of these, kingdom is the main division. Each kingdom is sub-division into group called phyla (singular-phylum). These are further divided into classes and orders, which consists of families. Families consist of genera (singular-genus), which include various species.