If you write 4/4 out in 8 quavers they fall into4 groups of 2: you could write them out like
/12/12/12/12/.
If you divide each main beat(ie each group of two quavers) into a triplet, the rhythm becomes
/123/123/123/123/ (verbally that would be diddley diddley diddley diddley). The way that would be notated would be12/8 (four groups of three in a 4-beat bar), which would save you having to write triplet signs over groups of notes. You normally wouldntbother, but if you want to notate swing rhythms (triplet based) accurately and unambiguously 12/8 does the job. It's surprisingly common to play in this swing rhythm, even if the ear doesnt always detect it.Michael Coleman playing a fast reel, for example, your ear will probably tell you he's playing the qquavers fairly evenly. In fact he's generating a huge drive by playing the firstnote of each pair twice as long as the second, ie he's in 12/8 time. But you'ld be being pedantic and time=wasting to write t out in 12/8, as you would be if you notated Bo Diddley beats or bodhran beats for reels in 12/8.For all normal usage 4/4 is perfectly satisfactory, and write a triplet in whenever there is actually a triplet of three notes played on one beat.
Sorry if this is longwinded and incomprehensible:I'd do better if I could play t you, or use musical notation. ..