According to the counterfactual view, X causes Y if and only if, without X, Y would not exist. Hume interpreted the latter as an ontological view, i.e., as a description of the nature of causality but, given the limitations of the human mind, advised using the former (stating, roughly, that X causes Y if and only if the two events are spatiotemporally conjoined, and X precedes Y) as an epistemic definition of causality. Having an epistemic concept of causality is needed to distinguish between causal and noncausal relations. The contemporary philosophical literature on causality can be divided into five big approaches to causality. These include the (mentioned above) regularity, probabilistic, counterfactual, mechanistic, and manipulationist views. The five approaches can be shown to be reductive, i.e., define causality in terms of relations of other types. According to this reading, they define causality in terms of, respectively, empirical regularities (constant conjunctions of events), changes in conditional probabilities, counterfactual conditions, mechanisms underlying causal relations, and invariance under intervention. Geometrical significance
Causality has the properties of antecedence and contiguity. These are topological, and are ingredients for space-time geometry. As developed by Alfred Robb, these properties allow the derivation of the notions of time and space. Max Jammer writes "the Einstein postulate ... opens the way to a straightforward construction of the causal topology ... of Minkowski space." Causal efficacy propagates no faster than light.Thus, the notion of causality is metaphysically prior to the notions of time and space.
Arachnoiditis is an inflammatory condition of the arachnoid mater or arachnoid, one of the membranes known as meninges that surround and protect the nerves of the central nervous system, including the brain and spinal cord. The arachnoid can become inflamed because of adverse reactions to chemicals, infection from bacteria or viruses, as the result of direct injury to the spine, chronic compression of spinal nerves, complications from spinal surgery or other invasive spinal procedures, or the accidental intrathecal injection of steroids intended for the epidural space. Inflammation can sometimes lead to the formation of scar tissue and adhesion that can make the spinal nerves "stick" together, a condition where such tissue develops in and between the leptomeninges. The condition is extremely painful, especially when progressing to adhesive arachnoiditis. Another form of the condition is arachnoiditis ossificans, in which the arachnoid becomes ossified, or turns to bone, and is thought to be a late-stage complication of the adhesive form of arachnoiditis. Signs and symptoms
Arachnoid inflammation can lead to many painful and debilitating symptoms which can vary  greatly in each case, and not all people experience all symptoms. Chronic pain is common, including neuralgia, while numbness and tingling of the extremities can occur with spinal cord involvement, and bowel, bladder, and sexual functioning can be affected if the lower part of the spinal cord is involved. While arachnoiditis has no consistent pattern of symptoms, it frequently affects the nerves that supply the legs and lower back.