People use the term “common sense” to support their way of thinking. If I say that I attempt to use common sense as much as possible I am referring to my own habitual mode of thought, which I assume is based mainly on adequate knowledge and some kind of logic. But “common sense is not that common” is a caveat we should all heed.
Common sense refers to that kind of thinking which is commonly used and agreed upon by most people. This seemingly makes it common to all, we suppose, when actually there is no agreed upon train of thought that all accept. (Take religion and politics for examples.)
Just consider the difference between objective thinking (”just the facts ma’am”) and subjective thought (which contains final meaning only for the individual). Truly logical thought is used by few people rarely. So common sense is not based on logic primarily. Common sense is based on common language usage.
This is why people who speak different languages do not always (or is it often?) make sense to each other, even in translation. Language contains inherent assumptions within its structure. Take English for example. Medieval English, for someone who has tried to read and understand it, betrays a different mind set compared with modern day English, and there are forms of English extant that suggest different world views entirely.
In the strictest sense, much of conversation does not attempt to make real sense at all. It is emotive rather than denotative. It depends on commonly shared feelings voiced agreeably, even when there is not necessarily any agreement as such (putting your feelings into words).
Scientific thought, strictly followed, would be common sense if it were widely shared. But scientific thought often allows two parties to understand what they disagee about mainly. Finding agreement through it is a much harder task. The narrowed thinking necessary for scientific discourse hardly allows it to be common at all.
So I will make a liberal claim about my own commonsensical manner of thinking. If I can express my thoughts clearly, and sometimes agreeably, then this is my own (un)common sense. And for you to talk with me, and I with you, we will have to agree that this will have to do, and I will have to grant your common sense the same status as my own.