I'm changing a document prepared in Plain TeX and I'm trying to get a brace to cover multiple lines for example:

S is P { cannot both be true (L. of Contradiction)  

S is not P { cannot both be false (L. of Excluded Middle)

I know how to do this in LaTeX but I am struggling to find a Plain TeX version. I have this so far which causes excessive whitespace and pushes the RHS almost off the page.

```
$ \vbox{ {\it S is P}\hfil\break
         {\it S is not P} } \left\{ \vbox{cannot both be true (L. of Contradiction)\hfil \break
                                         cannot both be false (L. of Excluded Middle).} \right. $

```

Does anyone have any suggestions? Thankyou.