人類天性中的直覺是認識事物、判斷是非和分辨真假非常重要的能力，但是它通常是『素樸的』，所以『概念的分析』也往往是一件『必要的』事。雖然面對『錯綜複雜』的現象，未經粹煉的『思想』容易誤入歧途 ，但是『直覺理解』的事物，常常流於『想當然耳』之過失。伽利略老年著作了一本『Discorsi e dimostrazioni matematiche』Mathematical Discourses and Demonstrations，據說是『思想實驗』的起始處︰
……
Salviati︰ If then we take two bodies whose natural speeds are different, it is clear that on uniting the two, the more rapid one will be partly retarded by the slower, and the slower will be somewhat hastened by the swifter. Do you not agree with me in this opinion?

Simplicio.︰You are unquestionably right.

Salviati.︰But if this is true, and if a large stone moves with a speed of, say, eight while a smaller moves with a speed of four, then when they are united, the system will move with a speed less than eight; but the two stones when tied together make a stone larger than that which before moved with a speed of eight. Hence the heavier body moves with less speed than the lighter; an effect which is contrary to your supposition. Thus you see how, from your assumption that the heavier body moves more rapidly than ‘ the lighter one, I infer that the heavier body moves more slowly.
……
這段對話用著想像分析、邏輯推導、討論演示著亞里斯多德的『重的東西動得快』的錯誤。概略的說，如果□與○二物重量不同，往同一個方向運動，□也跑得比較快，設想用一條繩索將這兩者連在一起，那快的應該會被拖慢，而慢的將會被拉快的吧。假使這是件事實，這樣『□+○』整體來看不是更重的東西嗎？難道它不與『重的東西動得快』矛盾的嗎？？

古希臘哲學家埃利亞的芝諾 Ζήνων 宣稱︰即使是參與了特洛伊戰爭古希臘神話中的阿基里斯 Achilles ── 希臘第一勇士 ── 也追不上領先一步之烏龜，因為

動得再慢的物體也不可能被動得更快的物體追上。因為追逐者總得先抵達被逐者上個出發點，然而被逐者此刻早已經前往下個所在點。於是被逐者永遠在追逐者之前一步。

『運動』的概念即使能直覺掌握，卻從來都不是簡單的，就像所有瞬刻都可以說它是『靜止』的『箭矢』，又為什麼不能歸結出『動矢不動』的結論的呢？？