Present Perfect (I have done) vs Past Simple (I did)

Present perfect (I have done) vs past simple (I did)

First, we need to decide whether to use the past simple (I did) or the present perfect (I have done). A useful why to decide which is correct is to ask yourself this question:

Rule 1: Am I referring to a time period that is completely in the past or a time period that starts in the past and continues up to now?

▪️ If the time period is completely in the past, use past simple.

▪️ If the time period starts in the past and continues up to now, use the present perfect.

Take a look at these examples.

• Yesterday, I completed three tasks. (past simple)
• So far this week, I have completed eight tasks. (present perfect)
• Last week, I completed 20 tasks. (past simple)
  

Example 1 uses the past simple because the time period—yesterday—is completely in the past. Yesterday has already completely finished.

In example 2, the time period—this week—is not over. When we are talking about a time period that starts in the past and continues up to now, we use the present perfect.

Example 3 is similar to example 1. The time period—last week—has finished and is completely in the past, so we use the past simple tense.

Note how these common time phrases usually go with a particular tense:   

Here are some more examples:

💡Recently, due to the pandemic, it has been difficult to source this material.

💡Recently, due to the pandemic, it has been difficult to arrange activities offline.

💡Since the last update, we have pushed onto step 9 of the process.

💡Since the last update, we have redecorated three more classrooms.

💡Last month, it was difficult to source the materials due to the pandemic, but recently it has become easier.

💡Last month, it was difficult to organize any of the activities, but recently it has become easier.

💡As of today, we have completed 26 of the target compounds.

💡As of today, we have completed 3 of the target projects.

💡We tried to run the reaction yesterday, but it failed.

💡We tried to get in touch with him yesterday, but couldn't.

💡Unfortunately, we still haven't established the cause of the failure.

💡Unfortunately, we still haven't received the test results.

💡At first, we thought the problem was due to the temperature, but we have tried it at lower temperatures without any success.

💡At first, we thought the problem was on our end, but we have tried using a different network without any success..  

💡Unfortunately, this week we haven't made as much progress as we expected.

💡Unfortunately, this week we haven't finished as many tasks as we expected.

💡We haven't received the materials yet.

💡They haven't arrived yet.

💡We've never workedon these types of compounds before.

💡We've never worked with this type of clients before.

Of course, we don’t always directly say the time phrase. It may be implied:

💡Have you finished the report? (This means “Have you finished yet?”)

💡I haven't worked on this kind of project before. (= In my whole career up to now)  

Rule 2: When something happened in the recent past and we are focusing on the result or situation now, we also use the present perfect.

This is common with decisions or problems. Often, we made the decision or met the problem a short time ago, but we are focusing on how it affects us now.

Here are a few examples:

💡Because of the problems with the original route, we have decided to switch to the backup plan.

💡Because of the changes in the system, we have decided to switch to the backup plan.

💡We've run into a problem with the purification step, so we may need some additional time.

💡We've run into a problem with printing out the materials, so we may need some additional time.

💡We have sent the samples to our analytical team to confirm the structures.

💡We have sent the invoices to the finance team.

However, if we include a time phrase in our sentence referring to the past, we have to change to the past simple:

💡We discussed this with our R&D team yesterday and decided to switch to the backup plan.

💡We discussed this with our supervisor yesterday and decided to switch to the backup plan.

💡We ran into a problem when we tried to purify the product.

💡We ran into a problem when we tried to collect more data.

💡We sent the samples to the analytical team for testing yesterday. We should get the results later today.

💡We contacted the person responsible yesterday. We should get the results later today.