Apparently there are 2 similar options when one wants to say "I think so" in german. When do you use "ich glaube schon" and when "ich glaube ja"? Is there a difference at all? I've heard my husband and other people using both.
As far as I understand, the original question is (considering the title of the threat); "ich glaube ja" vs. "ich glaube schon". (both without comma)
And these are indeed very similar.
Considering the style I expect "aber" behind "ich glaube ja ...".
Ich glaube ja, dass er für den Job geeignet ist, aber ist er nicht sehr jung?"
This "but" may be implicit. It is "I think so, (but)."
In case of "Ich glaube schon, ..." this "aber" (but) part may also be there, but there may be positive reasons. "Ich glaube schon, dass er geeignet ist. Er hat schließlich langjährige Erfahrungen auf diesem Gebiet." It is "I think so, (because).""Ich glaube schon, dass er geeignet ist, aber ist er nicht etwas jung?" - here it is the same as "Ich glaube ja." It is "I think so, (but)."
Note the big difference to
Ich glaube, ja. (complete sentence, I believe, yes.)
Ich glaube, schon. (The same, but more doubts.) Maybe you can omit the comma in front of "schon" But I would set it here. Otherwise it could mean "I believe already."
ich denke ja (short and non stressed "ja" as particle) (I think so, but ...)
ich denke, ja (long and stressed "ja" meaning "yes, I think so")