Present perfect or past simple?

It can be difficult to choose between the past simple and the present perfect. Both tenses refer to the past. However, in the present perfect, there is a connection to the present. Compare these two examples:

• She took her medication yesterday.
• She has taken her medication today.

In the first sentence, the action and the time period have finished. In the second sentence, the action has finished, but the time period has not. The difference is small, but in the second sentence, there is a connection between the past and now. The fact that she took her medication today is important, for some reason, now. 

In the example in the image, the past simple verb, 'saw, is incorrect because of the time phrase: 'to date', which means 'until now'. ‘To date’ implies that more treatment will follow. In other words, the time period is not finished. In such cases, present perfect tense should be used.

Time words used with the present perfect

Other time references such as ‘already’, 'yet', 'today', and 'this week/month/year' also indicate the time period is not finished. 

To date, Mehnaz has seen the speech therapist three times.

Here are some more examples:

Justin hasn’t seen a physiotherapist yet and is anxious about any pain the exercises may give him.

Advice to quit smoking has already been provided on numerous occasions.