Apr 162015

necessary vs sufficient causalityThere are so many words used to label certain philosophical concepts that I truly hate with a passion! I don’t hate the actual concepts themself, just what was, somewhere down the philosophical line, used to label such concepts. Often the labels I hate are the ones that use words that have ambiguous meanings elsewhere. This offers so much confusion to so many people.

When getting into the topic of free will, one must deal with the concept of causality. Within that one concept, there are many labels I disdain.  Today I’m going to address “sufficient” and “necessary” causality, as the understanding of these are important. The words “necessary” and “sufficient”, however, are anything but helpful. There are other ideas surrounding causality that have horrible labels as well, for example, “accidental” vs “essential” causality. And no, such words do not imply that a cause happens by accident or that one happens to be less essential to the output.

For now, let’s get into “sufficient” and “necessary” causality. If you are unfamiliar with how these terms are used in the philosophy of causality, it may intuitively feel that the word “sufficient” isn’t as strong as the word “necessary”, but that’s simply a failure of the labels. In layperson terms when someone says something was “sufficient” they are meaning it in the sense that it was just enough to make it. Was there enough people at the event? Meh, there was a sufficient amount of people, but more would have been better. Just understand that such a word isn’t even close to this for “sufficient causality”.

In philosophy, in any other context other than causality, the word “necessary” means that something is required. For causality, however, both necessary and sufficient causality talk about something being required in this sense. These differing usages just add more confusion.

You may ask why I even bother talking about the words “necessary” and “sufficient” for causality, why not just use what they refer to instead. I couldn’t agree with you more on that, and that’s what I prefer to do. But, and this is a big but, there are many people who, when debated with or when discussing the topic of causality, will bring up these words. And if you don’t know what they mean in the context of causality, those people can successfully stump you. This will be annoying, and more times than not those people don’t even understand such words either. This is why, even though many jargon words aren’t necessary, it’s important that people become at least somewhat comfortable with some of them.

In this article, however, I’m going to change the words entirely. Instead of the term “sufficient causality” I’m going to use “must lead TO causality” and for “necessary causality” I’m going to use “must lead FROM causality” . If we want to shorten these we can label them “ml-TO” and “ml-FROM”. Instead of words such as “sufficient” and “necessary” that are ambiguous and problematic, the “TO” and “FROM” gives all of the distinction we need, and you’ll soon see why.

So let’s talk about what must lead TO causality (sufficient causality) is first . All it means is that for a given cause, it must lead to a specific effect. In other words, if we have cause X, it must lead to a specific effect (say Y) and cannot lead to a different effect instead (say W). So if  X is the ml-TO cause of Y,  then the presence of X necessarily implies the presence of Y. However, another cause Z may alternatively cause Y.

Now let’s get into what must lead FROM causality (necessary causality) is. All this means is that for a given effect, such must lead from a specific cause. In other words, if we have effect Y, it must lead from a specific cause (say X), and cannot lead from a different cause instead (say Z). So if  X is the ml-FROM cause of Y, then the presence of Y necessarily implies the presence of X. The presence of X, however, does not imply that Y will occur.

ml-TO causality

  • If X –> Y then X–>W is impossible
  • Z –> Y is, however, possible.

ml-FROM causality

  • If X –> Y then Z –>Y is impossible
  • X –> W is, however, possible

If both ml-TO causality and ml-FROM causality is the case, then both X necessitates the effect of Y, and Y necessitates the cause of X, so we have:

Both ml-TO and ml-FROM causality

  • If  X –> Y then X–>W is impossible
  • If X –> Y then Z –>Y is impossible
  • There is no “however” 😉

Now that you have an idea of what these are, I want to briefly assess them, as I think ml-TO causality (or sufficient causality) is logically the case, but ml-FROM causality (necessary causality), at least as far as logic is concerned, isn’t.

Also, for the free will debate, it’s important to note that ml-TO causality is important for the topic, but ml-FROM causality is irrelevant. So why is ml-TO causality the case?

This stems into the logical problem that if it’s not the case, if X can be the cause of both Y and not the cause of Y (but the cause of W instead), then X contains self-contradictory causal variables. To understand this is more detail, please read this article and infographic:

causal contradiction

This makes ml-TO causality something that must be the case for any given cause. For the free will debate, this has some important implications, one being that if every event has a cause, that the causal lines can only follow the specific path dictated by ml-TO causality. There can never be an “either/or” situation, at least without an event that does not have a cause (which would be just as problematic for free will).

Sidenote: The effect (Y) encompasses all events that X produces, which could be one or many. Do not confuse the fact that we are addressing a single “Y” with such implying that it’s necessarily one thing, only that if there are many events that are in Y, all of those events must happen due to X.

So how about ml-FROM causality? This is a different situation, at least on the logical front. Logically, there is nothing that says that if we have an effect (Y) that different causal setups couldn’t lead to Y.  To understand why this logically is the case, read this article, particularly the example given in it:

Basically, we can imagine two different scenarios that output the very same effect. To simplify this down to a universe scenario, we can imagine a universe with only two fundamental particles that after they pop out of a big bang event collide together to form one single object heading in a specific direction at a specific speed. We can call this universe A. We can also imagine universe B in which the big bang event is such that it shoots out the combined particles so that no collision happens, and that combination is identical to universe A after collision.


Keep in mind that regardless if the laws of physics of our own universe would allow for such or not is irrelevant to whether or not such was logically possible. In regards to logic, there is nothing that prevents an identical effect from being the output of a differing cause. It may, however, be the case that with the laws of physics the way they are for our known universe, that each effect has some sort of “information remnant” of its cause that makes it different for each cause. This we don’t really know and such would be speculation. We just cannot rule in that ml-FROM causality is a logical requirement.

For the free will debate, however, this is of no consequence. And perhaps this is the more important thing to address, because there are people who often confuse “necessary” (ml-FROM) causality with “sufficient” (ml-TO) causality, as if the fact that we can’t logically conclude ml-FROM causality is the case, that we can’t logically conclude ml-TO causality is the case. Either that, or they think ml-FROM causality helps lead us to an “otherwise” situation in a causal universe, which it doesn’t. If the universe is entirely causal, then the only thing to account for is the fact that ml-TO causality, which must logically be the case, does not allow for the ability to have done otherwise.

Keep in mind that this is only addressing the nature of causality. If someone asserts that some events do not have a cause at all (what I call an acausal event in my book), that is something entirely different. I address both causality and acausality thoroughly in my book Breaking the Free Will Illusion. Acausality, though not logically impossible, does have many problems to contend with. And for the free will debate, any such event would be totally destructive to willing if such had an effect on our conscious thought.

I know these types of terms can be confusing, so I hope this article at least gives you something to think about regarding ml-TO (must lead to) and ml-FROM (must lead from) causality, otherwise known as the more jargon terms “sufficient” and “necessary” causality. Just keep in mind that if someone starts talking about causality not needing to be “necessary”, they aren’t suggesting that if cause X exists it doesn’t necessarily lead to Y. It does necessarily lead to Y, it just so happens that the necessity of relevance for the free will topic isn’t labeled “necessary” but rather “sufficient”. Just convert the word “necessary” to ml-FROM and “sufficient” to ml-TO causality and address how ml-FROM is entirely irrelevant to the understanding the we could not have, of our own accord, done otherwise. Only ml-TO causality is needed for that understanding.


Hey everyone. I just wanted to thank you for visiting by website! I don’t do this at the end of my posts very much, but want people to know the various ways they can reach me and be a part of this discussion. This blog here is all about the many aspects of free will debate, so if that is an interest of yours please subscribe. If you are already a hard determinist or hard incompatibilists who understands this important aspect of us not having free will as defined here, and you have a facebook account, also join the “no free will” facebook group where like minded individuals can discuss the fine points of this topic: no free will facebook group

Something personal you may not know about me, I don’t just do philosophy. I also play around with pen and ink line art, some pretty bizarre things that just pop into my head. If anyone wants to check some of that out I have this website for such: TricksPlace.com. And of course feel free to leave me a message or comment at any time. I’m very friendly and hardly ever bite! 😉

In regards to what I’m currently up to, I have a book in the works about secular ethics without free will. I’ve always planned on a book on morality/ethics, but knew that the free will topic is an important base understanding prior to one on ethics. Check out my first book on the free will topic because I put a lot of effort into it, illustrated parts, and even have dialogues within it to make the information digestible to the most number of people. And if you found it helpful, I’d love a good rating and quick review on Amazon.com!

That’s it for now. Again, thanks for stopping by! More later.



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'Trick Slattery

'Trick Slattery is the author of Breaking the Free Will Illusion for the Betterment of Humankind. He's an author, philosopher, artist, content creator, and entrepreneur. He has loved and immersed himself in philosophy since he was teenager. It is his first and strongest passion. Throughout the years he has built a philosophy based on analytic logic and critical thinking. Some of the topics he is most interested in are of a controversial variety, but his passion for the topics and their importance drives him to want to express these ideas to others. His other passions include pen and ink line art and digital artwork.

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  2 Responses to “Uncomplicating Necessary and Sufficient Causality (for the Free Will Debate)”

Comments (2)
  1. It’s really too bad that the words necessary and sufficient or any substitutes have to be used at all. Throwing the rock caused the window to break / replacing the glass will cause the window to once again keep out the rain and do other things windows are supposed to do.

    But instead of the “leads to” or “proceeds from” issue, I find the situational context of the word “cause” interesting (as in are we discussing the physics of the immediate situation and nothing else, complex chains of causality over time, individual human motivation, interpersonal relationships, economics?)

    • Yeah, it’s all the same causality, such is just addressing if one necessitates the other logically. Don’t even get me started on the word choice for a whole lot of jargon terms, such drives me crazy as philosophy and clarity need to go hand in hand, and such needs to be understood by everyone. There is way too much obscurity and ambiguity in academic philosophical language.

      As always, thanks for your visit and valuable input Ed.

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