The relationship of A causes B is how we understand causation. In truth, causation is rooted in the way we think. Causation is a fundamental and necessary form of reasoning used to construct and understand experience. For example, a spoon is tapped on a cup, and it makes a clunk. If a spoon is tapped on a cup again, it makes a clunk again. After the second time, it is right to anticipate the clunk. The first time there is no anticipation. The clunk is only heard. The second time, the clunk is heard, and a repetition is remembered. The third time the clunk is anticipated, heard, and remembered. If A 'tap' cause, then B 'clunk' effect, then A causes B. Consistent repetition of causal events A causes B determines an effect, and this allows us to order and give predictable meaning to life experience. There is a sequence of causation A then B then C then D. A segment of this sequence is B then C. If B cause, then C is the identified effect. If C is the effect, then B is the identified cause.
However, an infinite causal sequence cannot allow for the identification of cause and effect, or causal relationship. That is, in the sequence of causation A to D some cause must precede D cause. That being, A cause, the first cause in the sequence. However, if the causal chain flows back infinitely, then causal relationship, or the identification of cause and effect, will not be determined. Identification of cause will continually jump to the next regressive cause, that is, some cause will always precede another cause. So again, this will occur infinitely chasing but never landing on a single cause for the identification of the cause to the effect, or causation. However, reason empirically qualifies causation, and causal relationship, and therefore we cannot have infinite causation in regress because infinite causation in regress fails to identify causal relationship, and the first cause.
A first cause must exist. If a first cause did not exist, or was not known, then reason would not provide for the identification of A cause and its relationship to B effect. Moreover, causation is not only finite in regress but in advance. The singular causal event A causes B is finite. It is possible to argue one cause to all effects, or one causes all. One switch causes all street lamps to turn on. If one switch is connected to one thousand street lamps, then when the switch is turned on all one thousand street lamps turn on. If one causes one thousand, then one causes all, and therefore causation is finite. That is, if one can cause one thousand effects, then one can cause one million, one billion, one trillion, or all of them.
Classical mechanical interpretation does not satisfy human curiosity of the true nature of reality because it does not account for willful human interaction with the environment. Classical mechanical interpretation argues that particles move, and their movement is affected by other matter and agencies which exist or move in space and time. Particle matter is ontologically something. Particle matter is something that has movement and therefore is causal. Movement is dependent upon location. Classical mechanics explains the particle as a mathematical point. A point is located by drawing a line from one point to another. Drawing a line requires an origin. Any point can be an origin. The direction and length of the line determines the location. However, location cannot be known unless there are three points. Point B can return to point A or it can forward to point C. Location is determined as either not point C or not point A, located on the left or right. Rather than two points AB only, point A to point B and the reverse direction from point B to point A. Point A is known by location relative to two other points. A line from point A to point B gives length and direction. However, the three points A, B, C give location. Point A is located and, therefore, known to all points on line BC. See figure below.