Why did David Hume think repeated events do not prove a necessary causal connection?

David Hume argued that repeated events do not prove a necessary causal connection because such a connection is never directly observed in experience. When we observe one event (the cause) followed by another (the effect), we perceive only their "constant conjunction"—that they are contiguous in time and space and that one consistently precedes the other.1234

Hume maintained that the idea of a "necessary connection"—the belief that the cause must produce the effect—is not derived from any observable property in the objects themselves. Instead, this idea is a subjective product of the human mind. Through repeated experience, we develop a mental habit or custom of associating the two events. When we encounter the first event, our mind is psychologically compelled by this habit to anticipate the second.2415

Consequently, Hume concluded that causal inferences are not based on logical reasoning but on this feeling of determination. Because we cannot logically justify the assumption that the future will resemble the past, our belief in necessary connection remains a matter of custom rather than rational demonstration.1435