There are two forms of the past in Spanish. One indicates that an event continued happening for a period of time or was repeated. This is called the "imperfect" past. The word "imperfect" doesn't mean that there is a defect, it means the past event is "unfinished". The other past form in Spanish is what we call the "preterite". It indicates that an event took place at some point in the past. Let's look at some examples in English to see what we mean.

John used to sell cars.

In this case, are we speaking of a one time event or something that continued, or was repeated over a period of time? We can see that this isn't a single one time event at a point of time, and then it was done. He was selling cars over a period of time. We aren't pointing to a particular moment and saying that at that point something different happened which wasn't happening before, or it stopped happening at that point. As a matter of fact, we aren't really specifying a point in time.

Let's look at another example.

John was selling cars.

Again, we are seeing something which continued happening for a while and we can't point out a particular moment when something different happened that wasn't happening before.

When we say that something "used to happen" or it "was happening" we would use the "imperfect" past in Spanish. But now let's look at another way of expressing the past in English.

John sold cars.

Notice that here we use "sold" with the same meaning as "was selling" or "used to sell". We could say, "When John worked at the Ford dealership he sold cars". In other words, he continued selling cars for a period of time.

Now let's take another look at the form "sold".

John sold the car.

In this case it is obvious that we are speaking of a one time event and we can focus in on a particular moment. We could pin down a specific moment, when the money was exchanged or when they signed the bill of sale. This is the idea that we express with the "preterite". For most verbs in English we simply add "-ed" to the end of the verb for the past. In many cases, however, English uses unpredictable irregular forms for the past. The form "sold" would be an example of this. Actually, "sold" really means "selled" (although, of course, we don't actually say it that way). What's important to remember is that in English, the simple past can be interpreted to mean "used to do" or "was doing", but also it can mean a single one time event that took place at a particular moment in the past. This is what we want to focus on now.

Let's see another example of a contrast between the "imperfect" past and the "preterite" past in Spanish. First, let's assume that I have an ongoing medical problem such as asthma, diabetes, etc. Let's say there is a new drug store which has better prices which has just opened. A friend sees me in the new drug store and might ask me, "where did you buy the medicine before?" He could have asked, "where did you used to buy the medicine?" or "where were you buying it before?" In any of these cases, he would be asking me about a continuing or repeated action in the past. In this case I would use the "imperfect" past in Spanish (the middle of the verb would change "a" to "aba"). On the other hand, we could have a different situation. Let's say that last night I got a headache. I went to the drug store and bought a bottle of aspirin. One trip to the drug store, at a particular point in time (last night). In this case, if he asked me, "where did you buy the medicine?", he would not mean, "where did you used to buy?" I would say, "I bought the medicine", not meaning "I used to buy" or (back then) "I was buying", but rather, at a point in time (last night) I made a one time trip to the drug store and I bought (one time) the medicine.

Here are the forms that we use in the Spanish "preterite" forms to express one time events that took place at a particular moment in the past. Notice that instead of dividing the verb into three parts, we only have two parts, the stem and the ending. For now, we are going to focus on "A" category verbs.

PRETERITE

I spoke - yo hablé

you spoke - tú hablaste

he/she spoke - él/ella habló

we spoke - nosotros hablamos

they spoke - ellos/ellas hablaron

One point that it's important to notice. The preterite past form for "nosotros" looks and is pronounced exactly the same way that the present form would be. For example, "nosotros hablamos" could mean "we are speaking" or "we spoke". We would have to get the exact meaning from the context in which it is used in the sentence.

Let's break the forms down into stem and ending so that we can see a little more clearly how this form is constructed.

habl é

habl aste

habl ó

habl amos

habl aron

Now let's practice building some sentences in which we use the "preterite" past form of the verb to express a one time event at a particular point of time in the past.

I bought a gift (un regalo) for my friend.
Yo compré un regalo para mi amigo (mi amiga).

A female friend would be "amiga", but "mi" would not have to change. It can match either "o" or "a".

Did you buy a gift for your friend?
¿Compraste un regalo para tu amigo (tu amiga)?

Again, "amiga" would be used if we speak of a female friend, but "tu" would not change.
In these sentences, we are assuming that we are speaking to a friend with whom we would use a first name (the "tu" form, not the "usted" form).

Mary bought a gift for her friend.
María compró un regalo para su amigo (su amiga).

If the friend is a female, we would use "amiga". We would not have to change "su". It will match either "o" or "a".

There are times when we will have a spelling change in these "preterite" past forms. For example, if the verb ends in "-gar", we will have a spelling change in the "yo" form of the "preterite". This is because the letter "g" normally has a hard sound, like "go" in English. However, when "g" is followed by either "i" or "e", it has the "soft" sound, like the English letter "h". We want to avoid the sound change, so in Spanish, to keep the "g" hard like "go" when it is followed by "e", we add a silent letter "u" after the "g". By "silent" I mean that we don't actually pronounce it, like "oo" as in "school". It's just a signal to keep the "g" from changing to the "h" sound.

Let's practice some preterite past forms using verbs which end in "-gar".

Another case where we can have a spelling change is with verbs that end in "-car". Remember that the letter "c" normally has the sound of "k". However, if the "c" is followed by either "i" or "e", in Latin America it is pronounced like "s" (in most parts of Spain, it will be pronounced like "th"). We want to avoid this pronunciation change when we change forms within one verb. To avoid the "s" sound and preserve the "k" sound when followed by "e", we change the "c" to "qu".