One of the reasons English is often cited as one of the most difficult languages to learn is its many homophones, one of the most infamous pairs being “than” and “then.” What follows is an extremely simplified explanation of their proper use.
“Than” with an “a” expresses comparisons. One way to remember this might be to associate the “a” in “than” with the “a” in “comparison.” An example of the proper use of “than” would be:
Ian is taller than Sally is.
The above sentence compares Ian’s height to Sally’s.
“Then” with an “e” relates to time. One way to remember this might be to associate the “e” in “then” with the “e” in “time.” An example of the proper use of “then” would be:
Ian was the taller of the two children, but then Sally grew.
The above sentence helps express when in time Ian was no longer taller than Sally–after she grew.
A sentence that uses both “than” and “then” properly would be:
Ian was taller than Sally, but then Sally grew.