This is true in theory, but not in practice.

这在理论上是真的，但却不是事实。

youdao

And the second part of the book is devoted to India's speciality: ideas that have prevailed in theory, but not in practice, leaving reformers with nothing more to say, but plenty still to do.

本书第二部份著重探讨印度的专长：理论充满创意，却都没有实行，让改革家已经无话好说，却还有一大堆需要去做。

youdao

Prisoners have legal rights, but in practice these rights are not always respected.

囚犯虽有合法的权利，但实际上这些权利常未受到尊重。

《牛津词典》

Dr. David Hunter says he has not seen an increase in his practice as a pediatric ophthalmologist at Children's Hospital Boston.

VOA: special.2011.08.01

We can talk about "religion-ex" since everybody is spiritually equal, but women and men actually in practice are not equal.

我们可以说说“宗教性别“,在精神层面上，人人都是平等的，而实际上女人和男人是不平等的。

普林斯顿公开课 - 人性课程节选

The decay of Christian belief and practice is not a loss but rather an opportunity for poetry, in Crane.

基督教信仰和践行的衰败,在克莱恩看来，并不是损失，反而是诗歌新生的机会。

耶鲁公开课 - 现代诗歌课程节选

Understanding things in theory but not in practice is a common phenomenon with the government.

FORBES: American Political Economy Is No Different From English Language

Note that right at the outset the public interest comes first ( at least on paper, if not in practice).

FORBES: Have They Pushed the Self Destruct Button at the International Financial Reporting Standard Foundation?

In theory (although clearly not in practice) we are all subject to North Korean law on the wonderfulness of the dictatorship of the Kim family.

FORBES: Google's Move to Country by Country Censorship Breaks Disqus