Although may precede a proposition which is admitted as well as one which is doubted.
a. Although the children are, &c.
b. Although the children be, &c.
If, too, may precede propositions wherein there is no doubt whatever implied: in other words it may be used instead of since.
In some languages this interchange goes farther than in others; in the Greek, for instance, such is the case with εἰ, to a very great extent indeed.
Hence we must look to the meaning of the sentence in general, rather than to the particular conjunction used.
It is a philological fact (probably referable to the usus ethicus) that if may stand instead of since.
It is also a philological fact that when it does so it should be followed by the indicative mood.
This is written in the way of illustration. What applies to if applies to other conjunctions as well.
[§ 614]. As a point of practice, the following method of determining the amount of doubt expressed in a conditional proposition is useful:—