'That' in sentences

[Annimation]

I get really confused about the use of the word 'that' in sentences, for instance...
.

"As to their extreme stupidity, he deduced that this came from their being descended from generations of idiots."
--or--
"As to their extreme stupidity, he deduced this came from their being descended from generations of idoits."
.

...which is correct, and why please?

[emka]

Is this a vision test?

Sorry, but this font is so small that I can hardly read it even with my reading glasses on.

[TheParser]

I get really confused about the use of the word 'that' in sentences, for instance...
.

"As to their extreme stupidity, he deduced that this came from their being descended from generations of idiots."
--or--
"As to their extreme stupidity, he deduced this came from their being descended from generations of idoits."
.

...which is correct, and why please?

NOT A TEACHER


(1) Yes, it can be very confusing.

(2) "That" is not necessary when it only introduces a noun clause.

(a) I think that you are a good student./ I think you are a good student.

(Since you are a learner, I suggest that you always use "that.")

(3) Sometimes it is mandatory (you must use it).

(a) When it is the subject:

Is that your car that is parked outside? (Of course, you could NOT ask:

Is that your car is parked outside?)

(4) When it is the object, you often have a choice:

(a) What did you think of the soda that we drank last night? (That is, "We drank that last night." The word "that" = the soda.)

(i) Some native speakers delete (drop) the "that." I most respectfully suggest that you

use it.

(5) If you have a question about a particular sentence, please post it here. The

excellent teachers will be very happy to help you.

(I wish to credit Michael Swan's Practical English Usage for two of the sentences

(that) I used.)