Haec iam

[john abshire]

Haec iam exponam breviter ut scire possitis qua ratione comprehensa sint.

Now I will explain these things briefly so that you are able to know by what reason they ought to be understood.

 

[Pacifica]

There is not "ought" or "should" or "would"; the verb is subjunctive simply because it's an indirect question.

In this context (the uncovering of the Catilinarian conspiracy):

Ratio = way, manner.
Comprehendo = detect, discover.

 

[john abshire]

Haec iam exponam breviter ut scire possitis qua ratione comprehensa sint.

Now I will explain these things briefly so that you are able to know by what reason they ought to be understood.

I mistakenly thought that comprehensa sint was passive periphrastic.
Now I will explain these things briefly so that you are able to know by what manner they WERE understood/ detected.

edit: detected added for definition of comprehendo
Edit 2; are changed to WERE

 

[Pacifica]

Now I will explain these things briefly so that you are able to know by what manner they are understood.

Almost. But "are understood" is the wrong tense.

 

[john abshire]

Almost. But "are understood" is the wrong tense.

Changed are to WERE;
Semper providi quo modo in tantis insidiis salvi esse possemus.
I TOOK PRECAUTIONS BY what method we MIGHT be safe in SO GREAT A plots.

edits: in capital letters

 

[Pacifica]

provided/ foresaw

More like "took precautions (as to)".

what method

By what method, in what way, how.

we were able

Better in the context: "we might".

in plots of great size

Tantus, tanta, tantum = so great, such great.