-He stopped to think about the future. -He stopped thinking about the future. Are both sentences using Simple Past?
Yes both the sentences are in "Simple Past Tense" because main verb in both the cases is "stopped" which is (simple) past form. But the two sentences do not mean the same. In the first sentence physical action is involved - 'he' actually stopped (while walking or talking) to think about the future. In the second sentence mental action is involved. Hope I have answered your question. Thanks!