At its simplest, a "basis" (as the word "base") is the foundation upon which something rests.
Let me point out what should be obvious (and is extremely important to ME), and that is, when you speak of a "basis" for something, it means there are two (2) things under consideration. One thing is the "basis" and the other thing (that is, a certain "something ELSE") is that which is founded UPON that basis. There are two (2) matters to consider. The Merriam-Webster Dictionary says of "basis," "something on which SOMETHING ELSE is established or based." If you are asked, "What is your basis for what you say?" and your mind fails to understand that "something else" besides what you are saying is asked for, you are not understanding what the words "basis for" even mean. Two (2) things are in view. If you merely say to someone, "I want you to give me money," and he asks you, "On what BASIS do you think I should give you money?" you are mindless concerning English words if you answer him, "Because I WANT it - It's what I WANT." You have merely REPEATED your first statement, that you "want" money from him, and you have not AT ALL acknowledged the existence of a REASON for wanting it. Sadly, sometimes an ignoramus needs to be informed that "Because I WANT it" is no answer. It's not even TRUE, if you understand the simple meaning of "because." You cannot say "I want it because I want it." It is not TRUE that the REASON you want something is BECAUSE you want it. That's speaking gobbledygook. It's like saying "the shed caught fire BECAUSE the shed caught fire." You are saying NOTHING. Real ignoramuses often PHRASE that same stupid expression as "I just DO." We ask, "WHY do you wear snow shoes?" and the ignoramus replies, "I just DO." No productive conversation is possible with a person who cannot understand what "why" means, or what a "reason" is, or, what the "basis" for something is. "Why is it so hot in here?" is not answered by "Because it IS," or worse, "It just IS." This character astonishingly believes in a universe without "cause and effect." Nothing causes anything. Nothing is as it is, due TO anything else. Animals don't eat because they are hungry. No, "They just DO." Just as nonsensical is the ignorant wretch who cannot understand the concept of a "basis" for anything.
One of the things the American Heritage Dictionary of the English Language says for "basis" is, "A CONDITION FOR RELATING OR PROCEEDING." This is very much my meaning and usage of this word. The Heritage also follows that with these examples of usage in sentences: "a first-name basis; a friendly basis."
Webster's 1828 Dictionary of the American Language says of "basis": "1. The foundation of ANY THING; that on which a thing stands or lies; the bottom or foot of the thing itself, or that ON WHICH IT RESTS. 2. The ground work or first principle of something. 3. Foundation; support."
The Cambridge Advanced Learner's Dictionary says for "basis," "the most important facts, ideas, etc. from which something is developed." The word "something" there is rather vague. Allow me to substitute "a relationship." It will then define "basis" as "the most important facts, ideas, etc. from which a relationship is developed." If I put "an understanding" in place of "something" it will define "basis" as "the most important facts, ideas, etc. from which an understanding is developed." The Cambridge goes farther and enlarges on that first definition: "basis" is "a fact or situation that makes it possible for something to exist, happen, or develop in a particular way." That is very good: The BASIS for something to exist, happen, or develop is some specific "fact or situation." Again, see what happens when we get more specific than the word "something": If you'll allow me to substitute "A COMMUNICATION RELATIONSHIP" we get quite an INSTRUCTION for life: "The BASIS for 'a communication relationship' to exist, happen, or develop." That is, certain facts or situations CONSTITUTE THE BASIS for 'a communication relationship' to exist, happen, or develop.
If a complete stranger comes up to you in a parking lot and states "you should not own that make and model of a car - you should own a Ford, and it should be blue, and should have tinted windows," you will naturally be struck by the inappropriateness of that communication. But why is it inappropriate? Of course it has to do with this person and you being complete strangers. But the reaction you are having, this feeling that this communication is inappropriate, is really because there is no existing BASIS for this person to tell you that you should not own the car that you do, but own a blue Ford instead. This stranger is welcoming himself to be your counsellor or adviser or your life coach or something, but you see, you and he do not have such a relationship built between you. In other words there is no BASIS for him to critique what color of car you ought to own, much less to criticize your life. To such an odd communication out of a stranger a person might naturally respond, "Excuse me - Have we MET?" But what is that really asking? Your mind is searching for some "justification" for this person to be acting as though he has critiquing rights with you. You are looking for what BASIS the fellow imagines he has for even THINKING about what car you ought to have.
One last "stranger" analogy: Say you move to another state in the U.S. and to a small city that borders on forest and uncultivated country. Say you get all settled into your new place in town, and decide to go out hiking in the nearby woods. You trek an hour through the woods and across creeks and climbing over rocks, and then come upon a cabin the woods, and you can see immediately that whoever lives there has got chickens. Well you decide to continue on with your hike and you no sooner go another 50 yards when you see the apparent resident of the cabin, an old fellow fishing from the bank of a stream. "Howdy" and "Howdy" are exchanged, and you explain that you're out hiking, and you ask if he's the resident of yonder cabin where those chickens are, and he says he is. You ask him, "Are you fishing for dinner?" "Yup," he replies. And you say, "I don't think you should live in these woods and have chickens, and have fish for dinner out of that stream. That's just stupid. There's a perfectly good city over there, and you can get chicken and eggs and fish at the Safeway store. I think you should move to the city." Well of course I realize that reading this, you know how outlandish such behavior from you would be, and you would never have such an exchange with a stranger. But let me continue with the encounter: The old fellow replies to you: "So that's what you think I should do, is it? Change how I'm living? And do what you think I should? Sell my place, get rid of my chickens, and move to the city?" "Yes," you say. Well I'm sure you can think of any number of "responses" that one could reasonably expect from that old fellow. But regardless of what his reply might be, it would most certainly center on BASIS or "relationship" or both. If you and he are strangers, he is thinking that you do not have a "relationship" with him of such a nature as to tell him how to live. He is likely even feeling that it is inappropriate for you to even be FORMING THOUGHTS about how he lives. He might ask, "Well who are YOU?!" But there's another way of phrasing this "principle" that he feels you are violating, besides that your are not in such a "relationship" with him: it's that there is no "BASIS" for your critique of his life. It is the lack of a "basis" that makes voicing your opinions or critique so "off the wall," or "out of place," or INAPPROPRIATE. And nothing is going to make your voiced opinions in any measure seem "appropriate" except inasmuch as you can satisfactorily tell the man what the "BASIS" for your critique is.
What do you "BASE" your voiced opinions on? What is your "BASIS" for them?