Only then will I have a chance of achieving my dream

这句话的意思是,只有在那时,我才会有机会实现梦想.
only的倒装句.强调only后面的词或词组.
将only和only引导的词提前+助动词/be动词/情态动词+除了助动词/be动词/情态动词的原句.
原句是I will have a chance of achieving my dream only then.
例如 I read books only in the morning.变成Only in the morning do I read books.
He is a good boy only in his mind.变成only in his mind is he a good boy.
明白了吗?
if only是另外一种句式.表示：要是.该多好!后面要用虚拟语气.
If only there would be no school tomorrow!要是明天不上课该多好!