You could technically use them interchangeably, but there are differences (and hence times when you would use one over the other):

demo is used when starting a new sentence, so it cant be used as a conjunction between two sentences. (...ga tsuyoe. demo, watashi wa...)

keredo is shortened to kedo when not in a formal situation, and this one you use as a conjunction to connect sentences (watashi wa otoko no ko da kedo, anata wa....)

temo I haven't heard used, but someone said that its used at the end of a verb and has a meaning of "even if," and it acts as a conjugation (okane ga kakatemo, tanoshii - even if it costs money, it will be fun). to conjugate i thnk you just drop the -ru and add ttemo, not sure on the -u verbs or on your other question.

Spaztick wrote:temo I haven't heard used, but someone said that its used at the end of a verb and has a meaning of "even if," and it acts as a conjugation (okane ga kakatemo, tanoshii - even if it costs money, it will be fun). to conjugate i thnk you just drop the -ru and add ttemo, not sure on the -u verbs or on your other question.

Unfortunately I'm really picky about translations, and can be kinda hard-headed about it. It comes from listening to my English teachers give strange Japanese-English translations every day.

*Start Rant*

I mean dear god, why do they think that pretty means かわいい?!? Why do they teach this to my students, who then laugh if I tell them the mountains are pretty! I will destroy them and their butchering of my language!

I mean dear god, why do they think that pretty means かわいい?!? Why do they teach this to my students, who then laugh if I tell them the mountains are pretty! I will destroy them and their butchering of my language!

*End Rant* Sorry. just had to get that off my chest.

I hear you. I'm sick of having to explain that when I'm asking them:
"What kind of music do you like?"

that I don't mean:
「親切な音楽が好きですか。」

It comes from the stubborn desire to continue teaching language using 500-year-old methods. When you learn a foreign language via the Grammar Translation method you get stuck in the mindset that a single word in the native language has a single equivalent in the target language.

And yet after five decades of this method churning out generation after generation of Japanese who can't speak a lick of English despite 6+ years of study it hasn't occurred to anyone that the system they are using isn't worth shite!:@

>Ahem<

Sorry about that. I hadn't intended on adding quite so vehemently to your rant.