To have underline in two lines?

Command

\underline{bla bla ... bla}


The content overflows like so at the moment

How can you have underline without overflow to the margin?

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Don't use underlining for emphasis. –  egreg Feb 12 at 9:05

You can use \uline from ulem package:

\documentclass{article}
\usepackage[normalem]{ulem}
\begin{document}
\uline{As any dedicated reader can clearly see, the Ideal of practical reason is a
representation of, as far as I know, the things in themselves; as I have shown
elsewhere, the phenomena should only be used as a canon for our understanding.
The paralogisms of practical reason are what first give rise to the architectonic
of practical reason. As will easily be shown in the next section, reason would}
\end{document}


The option normalem is passed to prevent ulem from under lining the emphasised text.

Another option is to use \ul from soul package:

\documentclass{article}
\usepackage{soul}
\begin{document}
\ul{As any dedicated reader can clearly see, the Ideal of practical reason is a
representation of, as far as I know, the things in themselves; as I have shown
elsewhere, the phenomena should only be used as a canon for our understanding.
The paralogisms of practical reason are what first give rise to the architectonic
of practical reason. As will easily be shown in the next section, reason would}
\end{document}

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I always suspected you're a Kantian. –  egreg Feb 12 at 9:06
@egreg hehe, You suspicion is correct :) –  Harish Kumar Feb 12 at 22:53