If-openers
Sentence-starting words that set up a condition or follow from one, all built around -tara.
moshi
if; supposing
もし
Opens a sentence to flag a hypothetical, so the -tara / -ba / -nara / -te mo at the end is expected.
moshi ame dattara, yameyou.
If it rains, let's call it off.
もし雨だったら、やめよう。
moshi ame dattara, yamemashou.
If it rains, let's call it off.
もし雨だったら、やめましょう。
Moshi alone doesn't make an 'if'; the ending still has to be -tara, -ba, -nara or -te mo.
Learn first: -tara
dattara
polite deshitarain that case; if so
だったら でしたら
Starts a reply that builds a plan on what the other person just said.
dattara, ashita ni shiyou.
In that case, let's make it tomorrow.
だったら、明日にしよう。
deshitara, ashita ni shimashou.
In that case, let's make it tomorrow.
でしたら、明日にしましょう。
yokattara
if you like
よかったら
Softens an offer or invitation so it's easy to say no; goes at the start of the sentence.
yokattara, issho ni iku?
If you're up for it, want to come along?
よかったら、一緒に行く？
yokattara, issho ni ikimasen ka?
Would you like to come along?
よかったら、一緒に行きませんか？
Same word in desu/masu speech; yokereba is a touch more formal, yoroshikereba is keigo.