I have a setup in my preamble that allows this:
\documentclass[12pt]{report}% Not sure what this is for
\usepackage{array,ltablex, makecell}%
\newenvironment{conditions}
{\par\vspace{\abovedisplayskip}\noindent\begin{tabular}{>{$}l<{$} @{${}={}$} l}}
{\end{tabular}\par\vspace{\belowdisplayskip}}%This is for descriptions of equations
\usepackage[]{multirow}%Essential for cells in table spanning multiple rows
\usepackage{tabulary}% This is for tables
\usepackage{longtable,array,ragged2e}% This is formatting for long tables
\usepackage{tabularx,caption}
\newcolumntype{LL}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}%This is a wrapper to make everything a certain width -left aligned columns with stuff at the top.
\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}X}%This is a wrapper to make everything a certain width -left aligned columns with stuff at the top.
\newcolumntype{CC}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}%C is for central aligned columns and middle aligned.
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}X}%C is for central aligned columns and middle aligned.
\newcolumntype{R}[1]{>{\raggedleft\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\newcommand{\ra}[1]{\renewcommand{\arraystretch}{#1}}%This is for precision tables per property
\begin{document}
\begin{longtable}{@{}LL{6cm}LL{8cm}@{}}
\caption{Claims that are Difficult to Check}
\label{table:claimimpossible}\\
\toprule
\textbf{Example Sentence} & \textbf{Explanation}\\
\midrule
\endhead
\bottomrule
\endlastfoot
Long text...... & Long text......\\
\midrule
Long text...... & Long text......\\
\midrule
Long text...... & Long text......\\
\end{longtable}
\begin{table}[!htbp]
\setlength\extrarowheight{3pt}
\setlength\tabcolsep{4pt} % default value: 6pt
\catcode`_=13 % Make _ "active";
%% This setting expires at end of current group, i.e., at end of "table" environment
\def_{\textunderscore\hspace{0pt}} % "meaning" of "_"
\caption{List of Open and Closed Evaluation Properties}
\label{table:openclosed}
\ra{1.0}%This stretches the contents of cells
\begin{tabularx}{\textwidth}{|C|C|C|}
\hline
\textbf{Open Properties} & \textbf{Closed Properties} &
\textbf{Sentence Label Properties} \\
\hline
\begin{tabular}{@{}L@{}}
foreign_direct_investment_net_inflows\\
\end{tabular}
&
\begin{tabular}{@{}L@{}}
foreign_direct_investment_net_inflows\\
\end{tabular}
&
\begin{tabular}{@{}L@{}}
foreign_direct_investment_net_inflows\\
\end{tabular}\\
\hline
\end{tabularx}
\end{table}
\end{document}
The first table needs to have page breaks, and fixed column widths, hence I used a longtable. The second type of table needs to be flexible and have the option within its set up to wrap text based on characters such as _, as the word time_required_to_start_a_business will currently never wrap in a cell. However, it doesn't need to allow page breaks.
Currently I am getting an error on my longtable which is:
Package array Error: Illegal pream-token (4cm)
: `c' used.
See the array package documentation for explanation.
Type H <return> for immediate help.
...
l.23 ...in{longtable}{@{}LL{4cm}LL{4cm}LL{6cm}@{}}
Note, the second table came from this previous answer, which explains my use case for the underscore based text wrapping I want to achieve (note, preferably not for every table if possible):
Wrapping text in tables which contains underscores
The error is about the array package - I know I am loading this twice but is the error really about that?

LLandL. ChangeLLintoYor something. Same withCC, change intoBor whatever. – Runar Sep 03 '16 at 15:55LLandCCare illegal; consider usingKandBinstead. Moreover, the definitions of theLandCcolumn types are seriously flawed: It makes no sense to assign a variable parameter to them but then not use it -- as, sure enough, is done later on in the body of the document. Separately, it's very bad practice to re-use the column name typesC,LandRsince these are already defined by thetabularypackage, which is loaded by the code. However, do you even need thetabularypackage? – Mico Sep 03 '16 at 16:16tabularypackage as I never have atabularytable. What does{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}X}do? Is this a definition purely for thetabularXpackage, which thus doesn't allow variable parameters? I didn't use a variable parameter as the previous answer for the underscore table did not have such a variable parameter for theCtype? – Dhruv Ghulati Sep 03 '16 at 16:30tabularxenvironments only. But, no, you can use column types with variables in such tables. And, yes, the error is related to thearraypackage and, yes, you should look at its documentation as it will explain much of what is wrong and several of the comments made so far ;). – cfr Sep 04 '16 at 01:33\toprulewill probably give you an error, although I realise LaTeX is not getting that far at the moment. (Are the claims impossible? Or just difficult to check? Or impossible to check? If they are impossible, why would they need to be checked?) – cfr Sep 04 '16 at 01:36