a. 理论的, 理论上的, 假设的, 推理的【计】 理论的【经】 理论上的

◆记忆方法一：
谐音：四爷若太抠 四爷若太抠，就不会买理论的书籍。

theory/theoretical/practice/practical
记忆：
1. theory [ 5WiEri ] the-o-ry o,音“奥”，奥妙，趣味联想：理论是研究事物奥妙的学问；n. 理论, 学说 Karl Marx was the founder of the theory of communism.卡尔马克思是共产主义理论的创始人。
2. theoretical [ WiE5retikEl] adj. 理论上的 What he said was theoretical, not practical. 他的话纯属理论，不切实际。
3. practice [ 5prAktis] n. 实行, 实践, 实际, 惯例 It’s high time we put our plan into practice. 现在是该我们实施计划的时间了。 格言： Practice makes perfect.熟能生巧。
4. practical [ 5prAktikEl] adj. 实际的, 实践的, 实用的 Practical experience may not be theoretically right. 实际经验也许在理论上并不正确。
5. actual [ 5AktjuEl ] adj. 实际的, 真实的, 现行的 The actual operations tell the world what they really are. 他们的实际行动向世界表明了他们有真实面目。
另类阅读：
We must put the theory into practice. Otherwise, we don’t know whether the theoretical ideas are practical or not.
轻松一刻
Teacher: What do you think is the longest and what is the shortest?"
Student: The last few minutes in class is the longest and the last few minutes in an exam is the shortest.