Displaying an element similar to p inside a span?

Displaying an element similar to p inside a span?

I have a span with an inculded p, like this:
<span>
<p>this is the p</p>
</span>
This is not allowed according to the HTML5 specs. Now, my HTML is more
complex than the above and I need something similar to a p which I can use
instead. Which tag could I use or which element can I change using css so
it behaves like a p?