I think he is sick. 是你現在想,他現在正在病
I think he was sick. 是你現在想,他當時病了(當時是指著在你想的時間之前)
I thought he was sick. 是你在過去某個時間想,他在那時病了
I thought he had been sick.是你在過去某個時間想,他在那時之前的某個時間病了
1)I THINK HE IS SICK...這句本來語法就錯誤...應該是 i think he is sicking= 我猜他正在生病
2)i think he was sick= 我猜他之前病了
3)I thought he was sick= 我以為他之前病了(事實不是)
4)i thought he had been sick=我以為他病了一段時間(事實不是)
4)的用法是過去分詞, 表示是一段時間的, 這個用法有一個規則: 一定要寫時間: i thought he had been sick before last sunday. 過去分詞的用法是說 在以前的某個時間之前的一段時間
另外還有限在分詞, 表示是一段時間的, 這個用法有一個規則: 一定要寫時間, 現在和過去分詞的分別就是...現在分詞的時間寫法: since 1999, i have been in the usa. 過去分詞: before 1999, i had been in the usa.