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Causality, or causation, is the relationship between causes and effects. In common parlance, an event or state of affairs A is a cause of an event B if A is a reason that brings about the effect B. For instance, one might say "my pushing the accelerator caused the car to go faster". But this definition is somewhat circular; what does it then really mean to say that A is a reason that B occurs? An important question in philosophy and other fields is to clarify the relationship between causes and effects, as well as how (and even if!) causes can bring about effects.
David Hume held that causes and effects are not real (or at least not knowable), but imagined by our mind to make sense of the observation that A often occurs together with or slightly before B. All we can observe are correlations, not causations.
See also post hoc ergo propter hoc.
Real or imagined, Attribution Theory is the theory concerning how people explain individual occurances of causation. Attribution can be external (assigning causality to an outside agent or force - claiming that some outside thing motivated the event) or internal (assigning causality to factors within the person - taking personal responsibility or accountability for one's actions and claiming that the person was directly responsible for the event). Taking causation one step further, the type of attribution a person provides influences their future behavior.
The intention behind the cause or the effect can be covered by the subject of action (philosophy).
According to law and jurisprudence, legal cause must be demonstrated in order to hold a defendant liable for a crime or a tort (ie. a civil wrong such as negligence or trespass). It must be proven that causality, or a 'sufficient causal link' relates the defendant's actions to the criminal event or damage in question.
For a discussion of how causality resonates in the field of physics, see causality (physics)
In a strict reading, if A causes B, then A must always be followed by B. In this sense, sex does not cause pregnancy, nor does smoking cause cancer. In everyday usage, we therefore often take "A causes B" to mean "A causes an increase in the probability of B".
The establishing of cause and effect, even with this relaxed reading, is notoriously difficult, expressed by the widely accepted statement "correlation does not imply causation". For instance, the observation that smokers have a dramatically increased lung cancer rate does not establish that smoking must be a cause of that increased cancer rate: maybe there exists a certain genetic defect which both causes cancer and a yearning for nicotine.
Alternatively, A may be:
Aristotle suggested four types of cause: Material, Efficient, Formal and Final.
Consider the OSI Model as it applies to viewing this page on your machine.
The material cause of data transmission is the disk drives, routers, the network wiring, the detail of every microchip between server and client, and the phosphors or LCDs on your screen.
The efficient cause goes from bottom to top: HTTP messages are exchanges via a TCP connection. The TCP connection is established is via IP packets. The way that IP packets are transmitted is via (for instance) ethernet.
The final cause goes from top to bottom: the reason that the TCP connection contains what it does is becuse the HTTP session needs it that way. The 'reason' that that IP packet looks like that is because the TCP protocol requires it.
The formal cause is each separate protocol for the various layers.
Note that cause does not imply a temporal relation between the cause and the effect. See supervenience.
Also see, Causality and Structuralist Theory
Nihilists subscribe to a world-view in which the universe is nothing but a chain of meaningless events following one after another according to the law of cause and effect. According to this worldview there is no such thing as "free will", and therefore, no such thing as morality of a moral God. Learning to bear the burden of a meaningless universe, and justify one's own existence, is the first step toward becoming the "overman" that Nietzsche speaks of extensively in his philosophical writings.
As an appropriate "response" to the meaningless causality of the universe, nihilists recommend: courage and disillusion. Nietzsche's life provides an object lesson for those who are wary of nihilism, who maintain that such lives end quite typically in madness and chaos.
One of the classic arguments for the existence of God is known as the "First Cause" argument. It works from the premise that every natural event is the effect of a cause. If this is so, then the events that caused today's events must have had causes themselves, which must have had causes, and so forth. If the chain never ends, then one must uphold the hypothesis of an "actual infinite," which is often regarded as problematic, see Hilbert's paradox of the Grand Hotel. If the chain does end, it must end with a non-natural or supernatural cause at the start of the natural world -- i.e. a creation by God.
Sometimes the argument is made in non-temporal terms. The chain doesn't go back in time, it goes downward into the ever-more enduring facts, and thus toward the timeless.
Karma is the belief held by some major religions that a person's actions cause certain effects in future incarnations, positively or negatively.
Some modern religious movements have postulated along the lines of philosophical idealism that causality is actually reversed from the direction normally presumed. According to these groups, causality does not proceed inward, from external random causes toward effects on a perceiving individual, but rather outward, from a perceiving individual's causative mental requests toward responsive external physical effects that only seem to be independent causes. These groups have accordingly developed new causality principles such as the doctrine of responsibility assumption.
The classic IF/THEN statement in most programming languages is a perfect example of simplified causality: If A is true, then B will occur. This can be expanded using Boolean algebra: If A and B are both true, then C will occur; If either A or C is true, then C will occur.
In statistics, it is generally accepted that observational studies (like counting cancer cases among smokers) can give hints, but can never establish cause and effect. The gold standard for causation here is the randomized experiment: take a large number of randomly selected people, divide them into two groups, force one group to smoke and prohibit the other group from smoking (ideally in a double-blind setup), then determine whether one group develops a significantly higher lung cancer rate. Obviously, for ethical reasons this experiment cannot be performed, but the method is widely applicable for less damaging experiments.
That said, under certain assumptions, parts of the causal structure among several variables can be learned from full covariance or case data by the techniques of Path analysis and more generally, Bayesian networks. Generally these inference algorithms search through the many possible causal structures among the variables, and remove ones which are strongly incompatible with the observed correlations. In general this leaves a set of possible causal relations, which should then be tested by designing appropriate experiments. If experimental data is already available, the algorithms can take advantage of that as well.
While the names we give objects often refer to their appearance, names and other symbols can also refer to an object's causal powers - what that object can do, the effects it has on other objects or people. David Sobel and Alison Gopnik from the Psychology Department of UC Berkeley designed a device known as the blicket detector which suggests that "when causal property and perceptual features are equally evident, children are equally as likely to use causal powers as they are to use perceptual properties when naming objects".
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