THE COMMA SPECIAL USES OF 'WHICH' There are three cases when 'which', and not 'that', is the only relative pronoun that can be used:   1. NUMERATOR + of + which Always use 'which' a quantity expression with 'of'. Note that these expressions require 'numerators' and are always divided from the rest of the sentence by a comma before and at the end of the relative clause. Finland has a diversity of ecosystem types, each of which can be broken down into many finer categories. The report details projected changes affecting everything from agriculture to breeding grounds for migratory birds, many of which are considered endangered. In 2002, the global temperature record was broken by a half degree Fahrenheit, which in climatic terms is a huge leap. Previous hot years, the last two of which were 1996 and 1998, broke the record by small fractions of a degree. Each student room is equipped with broadband Internet access available, the cost of which is included within the residence fee. Similar to 'which', the relative pronouns (whom whom), used for referring to people, can also be used in the same way as 'which': FinnCorp has 15 shareholders, none of whom have a clear majority or a leading role in the company.     2. PREPOSITION + which Always use 'which' directly after prepositions. Although 'which' typically introduces 'non-essential' information or comments, after a preposition, 'which' occurs without a comma and gives 'essential' information that defines and restricts the meaning of the word that comes before it. Each species and genus of plants produces pollen grains that have a distinct shape. These shapes can be used to identify the type of plant from which they came. A non-falsifiable theory is a hypothesis for which no test can be devised. Global warming theories attempt to account for the documented rise in average global temperatures since the late 19th century and assess the extent to which the effects are due to human causes. Even without a detectable increase in global temperatures, greenhouse gases could change circulation and weather patterns on which most of the world's population depend for their day to day survival. One potential change is the drying out of the Amazon Basin. Recently, scientists have documented trends in which the natural timing of animal or insect life cycles changed and the plants on which they depended did not.     3. REFERRING TO THE WHOLE OF A PREVIOUS CLAUSE In addition to referring to objects, 'which' can also comment on the whole of a previous clause. This fuction can not be carried out by 'that'. He managed to survive in Lapland for three weeks without food, which was amazing in light of the harsh winter temperatures.   In this example, it is not the lack of food that was amazing, but the fact that he survived in Lapland for three weeks without food - the whole situation referred to in the clause.

Finnish Virtual University / © 2004 Stotesbury, McAnsh & Pennington