Synthesis is the method where we study what the system actually does, and then combine or collide separate elements or components in order to form a coherent framework that describes the whole system, possibly inferring the existence of possible constituent parts or sub-systems that might be needed to enable the System to act in this way.
Analysis is the method by which we break down a Complex System into the parts or components which somehow combine to produce the system's overall behaviour. It is the study of the system's internal structure and processes and the connections or relationships between its component parts
Systems are intellectual or physically Whole entities, which need to be considered from the point of view of what the system performs or accomplishes. Analysis and Synthesis go hand in hand in understanding Systems. Which one you use first depends on what knowledge you have to begin with. We always eventually have to pull apart a System to look at its internal workings in order to understand it. BUT we shouldn’t start there, especially if the process is destructive, and by breaking it open to see inside, we would actually destroy the very thing we’re trying to understand. So we reverse the process: instead we look at what the system actually does or accomplishes - or SHOULD do and accomplish, and then theorise about what it makes it work like that. In order to do that we must figure out the actual problem that gets solved by the system, in order to figure out how it solves the problem.