Both x and y have to be measurable. Here, x could be score on IQ test. Since score on IQ tests are somewhat well correlated with academic achievement, then more

Both x and y have to be measurable. Here, x could be score on IQ test. Since score on IQ tests are somewhat well correlated with academic achievement, then more x (higher IQ score) means more likely y (higher academic achievement). It’s important to note that it’s only more likely. Correlation is a predicter of a relationship given a population, not a dictator of outcomes for individuals.