指示代词：各个代词的指代功能
1) 形式：
(1) this/that及其复数形式these/those，用于指代名词、短语和句子。
(2) same/such没有性，数，格的变化。
(3) so没有性，数，格的变化。
2) 句法作用：
(1) this/these和that/those的用法：分别用于在空间和时间上的进指和远指。
① 作为先行词用法的that和those中，those能指人和物，that 只能指物，且表单数。
② that/those，this/these可用来替代前文明确的名词及名词短语。
③ This和that可以作为状语表示程度。
注：one表示泛指，that和it 表示特指。that与所指名词为同类，但不是同一个，而it 与所指名词为同一个。
The hat you bought is bigger than that I bought.
I can't find my hat. I think I must buy one.
I can't find my hat. I don' t know where I put it.
(2) such，(the)same的用法
二者单复数相同，在句中可做主语、宾语、表语和定语。
Such was my immediate impression.
She said the same thing all over again
His illness was not such as to cause anxiety.
(3) so的代词用法：只用于两种情况
① believe，expect，hope，suppose，think，do等表示看法，假设和行为的动词之后，代替上文一个肯定陈述句。
② 用于系动词之后，替代表语。
Eg: Are you going to play football tomorrow? I hope so.
He is a lazy boy and will always be so.