Reflect on-means thinking of what happened in the past Contemplate-means to second guess and rethink about something . Ponder-means to think for a long period of time and to think of something very carefully. Ruminate-means to think deeply about something. (These words have similar meaning ,in the English language we call these words synonyms)

They are all very close in meaning, although "reflect on" refers especially to thinking about the past. Mishka gave good definitions. "Ruminate" is the least common word. Literally, "ruminate" refers to the way cows chew their food.

Hi Lilith I hope this helped. Have a great day💫.

They are all quite similar. I think seeing them in context would clarify the differences.