Conjugating English verbs is fairly simple. Most verbs add -ed to for the past and past participle tense. Let's take the infinitive 'to play' as an example.
Today, I play. ~ Yesterday, I played. ~ In the past, I had played.
That was easy, right? Problems usually arise when dealing with the pesky verbs that don't follow the rules. Ex: Swim, swam, swum. Let's start with one that many people—even the fairly grammar-conscious—often get get wrong: properly conjugating the infinitive 'to drag.'
The present tense is 'drag.'
Ex: Drag that chair over there, would you?
The past tense is 'drug,' right? Nope. It's 'dragged.'
(And don't worry. I'm not laughing at you. I correct myself on this one all the time.)
Ex: I scowled at my roommate sitting with a Coke in his hand and his feet propped on the coffee table, but I dragged the chair where he wanted it anyway.
Are you freaking out and dreading combing through multiple manuscripts for this mistake? Don't. To fix, simply do a document search for the word 'drug,' then replace any you used to mean dragged with 'dragged.'
Another verb can-o-worms is 'lie' versus 'lay.' Not only is the past tense of one the present tense of the other, but these verbs are not interchangeable. (For the sake of this lesson, we're going to exclude the 'lie' that means to be untruthful.) Here are the basic tenses of both.
Examples for 'lie': Today, I lie down to take a nap. Yesterday, I lay down to take a nap. In the past, I had lain down to take a nap.
Now 'lay': Today, I lay the pen on the desk. Yesterday, I laid the pen on the desk. In the past, I had laid the pen on the desk.
Hope that helps. For a list of irregular verbs and their basic tenses, click here.