1. 兩者均可指人，有時可互換(包括當先行詞為 all, anyone, someone等，同時也包括先行詞受the only等的修飾時)：
All that [who] heard him were delighted. 所有聽了他講話的人都很高興。
He is the only one among us that [who] knows Russian.他是我們中間唯一懂俄語的人。
Anyone who [that] is over sixteen is allowed in. 任何超過十六歲的人都允許進去。
It is impolite to turn your back on someone who [that] is speaking to you. 人家跟你說話，你把背朝人是不禮貌的。
2. 但是在下列情況，通常要用 that：
①當先行詞是一個既指人又指物的並列片語時：
I made a speech on the men and things that I had seen abroad. 我就我在國外所見到的'人和事作了報告。 ②當先行詞是who時(為避免重複)：
Who was it that won the World Cup in 1982? 誰贏得了1982年的世界盃?
③當關系代詞在定語從句中作表語時(可省略)：
Tom is not the boy (that) he was. 湯姆這孩子已不是以前那個樣子了。
3. 但是在下列情況，通常要用 who：
當先行詞為 those 且指人時，英語習慣上要用 who 來引導定語從句。如：
Those who do not wish to go need not go. 不願去的人不需要去。
Those who couldn’t walk were carried on stretchers. 那些不能走的人都用擔架抬著。
It is said that eat the most are the least healthy. 據說吃得最多的人身體最差。
Only had booked in advance were allowed in. 只有那些預先訂票的人可以進去。
The plan was supported by those who wished to listen to more good English. 這計劃受到想多聽好英語的人的支援。
Let us spend a few moments in silence so that / in order that we remember died to preserve our freedom. 讓我們默哀片刻，以緬懷那些為維護我們的自由而犧牲了的人們。
注：偶爾也可見到在 who 之後用 that 引導定語從句的用例，但相當少見。如：
The danger is that people who pay their bills on time will be lumped in with those that don’t. 危險的是那些及時付賬的人將會同那些不及時付賬的人混在一起。
