Now that you're studying English at a higher level, you need to be able to talk about the language itself.

One of the biggest areas of confusion for students is the difference between the past tense and the present perfect.

tense 英[tens]美[tens] adj.紧张的; 担心的; 不能松弛的; 令人紧张的(或焦虑的、满腹愤懑的等); 绷紧的; 拉紧的; 紧的;

n.(动词的)时; 时态; v.(使肌肉)拉紧; 绷紧;

present perfect  n.现在完成时

The past tense is indicated by use of the past tense marker, represented here by V(d).   

过去时用过去时标记来表示，这里用V(d)表示。

indicate 英[ˈɪndɪkeɪt]美[ˈɪndɪkeɪt] v.表明; 显示; 象征; 暗示; 间接提及; 示意; 指示; 写明; （用灯光或手臂）打行车转向信号; 有必要;

represent英[ˌreprɪˈzent]美[ˌreprɪˈzent] v.代表，表示; 代理（个人或团体）; 代表（个人或团体）出席; （在竞赛或体育赛事中）代表（国家或地区）; 象征; 使有代表性，使有代表作; 作为……的代表（代言人）; 表述; 描绘，（形象地）表现，描写; 使呈现; 集中地体现; 典型地反映; 陈述，诉说; 抗议说; 演出，扮演; （标志或符号）意味着，代表着，标志着; 相当于，相等于; 想象，设想; 回想; 提出异议，提出抗议; 再赠送; 再呈现; 再提出; 再递交; 再上演，再演出; 维护……的利益; 成为……实例，成为典型; 作为……的象征; 展示;

Here are some examples of regular verbs and their past tense forms.

So, as you can see, for regular verbs the past tense forms is indicated by the addition of an -ed at the end of the verb.

However, some of the most common verbs in English are irregular, so it is important to learn them.

irregular 英 [ɪˈreɡjələ(r)]  美 [ɪˈreɡjələr] adj.不整齐的;不平整的;参差不齐的;不规则的;无规律的;紊乱的;不正常的;不合乎常规的;（形式）不规则的;非正规军的 n.非正规军军人

Here are some examples

altogether there are over 200 irregular verb in normal use

Many people think that the past tense form only indicates past time.

However, that is only one of the possible meanings.

The past tense form is also used to express something that is unlikely or imaginary, from the speaker's point of view.

从说话者的角度来看，过去式也用于表达不太可能的或想象的事情。

Here is an example: "He wishes he had a car."

The fact is that he doesn't have a car, so the use of "had" indicates that it isn't real:it's imaginary.

“If he had a car, he could drive us to school.”

Again, "he doesn't have a car, so he can't drive us to school."

This condition expresses something that isn't a fact.

It's a counter-factual condition, which means it goes against what we know or believe.

这是一种反事实条件，这意味着它与我们所知道或相信的相悖。

counter-factual  反事实的

counter 英 [ˈkaʊntə(r)]  美 [ˈkaʊntər] n.(商店、银行等的)柜台;(某些棋盘游戏的)筹码;(电子)计数器，计算器;反对，反驳

v.反驳;驳斥;抵制;抵消 adv.逆向地;相反地;反对地 adj.反对的;一对中之一

factual 英 [ˈfæktʃuəl]  美 [ˈfæktʃuəl] adj.事实的;根据事实的;真实的

Both sentences are correct, but there is a difference in meaning.

In the top sentence, the condition that she waits is more likely from the speaker's point of view.

In the bottom sentence, the speaker thinks it's less likely that she's going to wait.

（There is going to be a sale next week，so I hope she doesn't go shopping tomorrow.）

（If that flight leaves on time，we're going to miss it，so let's run.）

（There was a big sale last week，so we all went shopping.）

（If that flight left few minutes later，we could take the next shuttle bus.）