Which is Larger?

What is assumed when two fractions such as 1/2 and 1/3 are compared to determine the larger? Does this same assumption hold when two ratios such as 1:2 and 1:3 are compared?

Extension
Generalize this result and compare 1/n with 1/(n+1) for all positive integers. How does 1:n compare to 1:n+1 ?