Synthesis is the opposite of analysis. When you analyze, you break a whole into its parts and examine how the parts relate to one another in order to judge the quality of the whole. When you synthesize, you start with different, unrelated parts, and search out relationships in order to put the parts together to make a new whole. You synthesize automatically when you read, as you relate “new” text information to previous knowledge and create the new “whole” of your knowledge in a field. Synthesis becomes more of a conscious act when you write, since you have to actively select pieces of information that make sense together. As The American Heritage Dictionary states, synthesis means “the combining of separate elements or substances to form a coherent whole.”
The concept of a “coherent whole” is essential to synthesis. When you synthesize in writing, you examine different types of information (ideas, examples, statistics, etc., from different sources) and different themes (perspectives and concepts) from different sources with the purpose of blending them together to help explain one main idea. So you have to look for relationships 1) among the sources’ themes and 2) between these themes and your own ideas in order to blend all of the pieces to make a coherent whole.
The concept of a “coherent whole” is important in terms of language, too. Once you examine content and choose the parts to synthesize, you need to express those parts in your own language in order to create a coherent whole in terms of writing style.
Synthesis is like combining different ingredients to make a stew. If you choose and combine carefully, with the end result (supporting your main idea) in mind, the ingredients will be both separate and well-blended, with all ingredients contributing as they should to the final taste.
View the following video for a basic definition of, and introduction to, the concept of synthesis.