If only 表示虚拟语气,如
If only I were you!如果我是你.
If only (expressing a strong wish表示强烈的愿望)但愿,真希望,只要...就好了：
If only he wouldn't eat so noisily.但愿他吃东西不这样大声就好了./If he would only learn to eat quietly!但愿他学会吃东西时小声点就好了!