[Grammar] I must have taken those pills twice a day.

[NAL123]

Speaking of a company's age requirement,

(1) To apply for the job, the candidate must have been born on or before 1st Jan. 2000. ("must" implies obligation/necessity)

(2) I had to take those pills twice a day. (obligation/necessity)

(3) I had to have taken those pills twice a day. (obligation/necessity)

(4) I must have taken those pills twice a day. (obligation/necessity)

Are sentences (1), (3) and (4) correct?

 

[SoothingDave]

3 and 4 are unnatural. 4 sounds like you have forgotten whether you took them or how often you did, but you are surmising that you did.

 

[NAL123]

3 and 4 are unnatural. 4 sounds like you have forgotten whether you took them or how often you did, but you are surmising that you did.

One more question, please:

Do these mean the same thing:

5) Do you remember that hilarious speech that Jack made at his wedding? It doesn't sound amusing when you repeat it, but it was so funny at the time. You had to have been there. [to appreciate how funny it was].

6) Do you remember that hilarious speech that Jack made at his wedding? It doesn't sound amusing when you repeat it, but it was so funny at the time. You had to be there. [to appreciate how funny it was].

 

[probus]

The tense in 5 is the formally correct one but you often hear 6 in American English.

 

[Rover_KE]

... and in colloquial English of any variety.