Biblatex: Using "and" within textcite, "&" within parencite, "&" within bibliography

Question

I am very new to LaTeX as you will see from my crude MWE. I have spent a lot of time tweaking biblatex to how I need it to look. I have one final problem, I can not find a work around and can't find a solution on the site.

I would like to show an "and" for my \textcite when there are multiple authors, which it currently does. Although I would like to have "&" for my \parencite with multiple authors. I would also like to have my bibliography showing "&".

Please find MWE and any help would be appreciated.

\documentclass[12pt, twoside]{report}
\usepackage{filecontents}
\usepackage[%
    backend=biber,
    style=authoryear,
    uniquename=init,giveninits,giveninits=true, terseinits=true,hyperref]{biblatex}
\usepackage{xpatch}

\DeclareNameAlias{sortname}{last-first}%Surname first

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 %\ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  %\addspace\&\space}

\newcommand{\biband}{\ifcurrentname{labelname}{\bibstring{and}}{\&}}

\renewcommand*{\finalnamedelim}{%
   \ifnumgreater{\value{liststop}}{4}{\finalandcomma}{}%
   \addspace\biband\space}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


\renewcommand{\labelnamepunct}{\addcomma\addspace}%Sets comma
\renewcommand*{\newunitpunct}{\addcomma\space}%Sets commas


\setlength{\bibhang}{0em}%remove indent
\setlength\bibitemsep{\baselineskip}% add vertical space

\begin{filecontents}{\jobname.bib}
@article{test,
 author = "Family, Given and Second, A and Given, Two",
 title = "title",
 journal = "Journal",
 year = "2012"}

 @Article{leis2016,
  Title                    = {A Temperature Compensation Technique for Near-Infrared Methane Gas Threshold Detection},
  Author                   = {J. Leis and D. Buttsworth},
  Journal                  = {{IEEE} Trans. Ind. Electron.},
  Year                     = {2016},
  Month                    = mar,
  Number                   = {3},
  Pages                    = {1813--1821},
  Volume                   = {63},
  File                     = {ieeetie-2016.pdf:PDF},
}

\end{filecontents}

\addbibresource{\jobname.bib}

\begin{document}


I would like to use {\bfseries ``\&''} within the {\bfseries bibliography}. \\
I would like to use {\bfseries ``and''} in {\bfseries textcite} \textcite{leis2016} \\ 
I would like to use {\bfseries ``\&''} within {\bfseries parencite} \parencite{leis2016}.\\

Example of three authors would be the same as above \textcite{test} using {\bfseries ``and''} within {\bfseries textcite}. \\

Although using {\bfseries parencite} to be {\bfseries ``\&''} \parencite{test}. 

\renewcommand{\bibname}{REFERENCES}

\xpatchbibmacro{date+extrayear}{%
  \printtext[parens]%
}{}{}

\printbibliography

\end{document}

Answer 1

Change of the final name delimiter between \parencite and \textcite from "&" to "and" as in

(Sigfridsson & Ryde, 1998) and Sigfridsson and Ryde (1998)

is a feature of APA style. See for example https://blog.apastyle.org/apastyle/2011/01/writing-in-text-citations-in-apa-style.html and https://blog.apastyle.org/apastyle/2011/02/changes-parentheses-bring.html.

If you are looking for a complete implementation of APA style with biblatex, you may be interested in biblatex-apa, which when loaded as

\usepackage[backend=biber, style=apa]{biblatex}

should produce a bibliography and citations according to APA guidelines.

The answer below shows how to change the final name delimiter in the standard styles.

With the new context sensitive delimiter interface that should be as easy as redefining finalnamdelim in global scope to give an ampersand and to give "and" for textcite.

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authoryear, backend=biber]{biblatex}


\addbibresource{biblatex-examples.bib}

\DeclareDelimFormat{finalnamedelim}{\addspace\&\space}
\DeclareDelimFormat[textcite]{finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\bibstring{and}\space}

\begin{document}
\cite{sigfridsson,companion}

\parencite{sigfridsson,companion}

\textcite{sigfridsson,companion}

\printbibliography
\end{document}

Edited to use the context sensitive delimiter interface. See the edit history for older versions of biblatex.

Answer 2

Biblatex supports context-sensitive delimiters; i.e. depending on the citation command used (\textcite, \parencite, etc), you can tell biblatex to use a different delimiter, for certain delimiter types. See §3.10.2 of the biblatex manual for more details.

\finalnamedelim is the delimiter used to separate (the last) two names in a citation or bibliography entry. Unfortunately, \finalnamedelim is not context sensitive by default, but we can easily change that:

% Modify name:delim to use a context-sensitive version of finalnamedelim
\xpatchbibmacro{name:delim}
  {\lbx@finalnamedelim{#1}}
  {\printdelim{finalnamedelim}}
  {}{}

% Set the global context to use an ampersand
\DeclareDelimFormat{finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\&\space}

% Set the textcite context specifically to use the "and" string
\DeclareDelimFormat[textcite]{finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\bibstring{and}\space}

How this works

According to the biblatex documentation, \finalnamedelim is:

The delimiter printed instead of \multinamedelim before the final name in a name list. The default is the localised term ‘and’, separated by interword spaces.

It is defined in biblatex.def as:

\newcommand*{\finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\bibstring{and}\space}

Note that the implementation is different in Spanish.

In all the standard styles, it is called via the name:delim bibmacro, which also defined in biblatex.def:

\newcommand*{\lbx@finalnamedelim}[1]{\finalnamedelim}
\newbibmacro*{name:delim}[1]{%
  \ifnumgreater{\value{listcount}}{\value{liststart}}
    {\ifboolexpr{
       test {\ifnumless{\value{listcount}}{\value{liststop}}}
       or
       test \ifmorenames
     }
       {\multinamedelim}
       {\lbx@finalnamedelim{#1}}}
    {}}

So, to make name:delim use a context sensitive version of \finalnamedelim, we need to use \printdelim{finalnamedelim} instead of \lbx@finalnamedelim{#1}. You could make a complete copy of name:delim and change only that line, or you can use the xpatch package to selectively replace only the part you care about:

\xpatchbibmacro{name:delim}
  {\lbx@finalnamedelim{#1}}
  {\printdelim{finalnamedelim}}
  {}{}

The final step is to now declare the delimiter format for each context using DeclareDelimFormat[<context>]{<name>}{<code>}.

If you don't specify a context, then the format will apply globally (i.e. to any context that doesn't have a specific format set). Hence, the following will force an ampersand to be used for all contexts unless otherwise specified:

\DeclareDelimFormat{finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\&\space}

And now we override the \textcite context:

\DeclareDelimFormat[textcite]{finalnamedelim}{%
  \ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
  \addspace\bibstring{and}\space}

\bibstring{and} keeps this language sensitive, and also allows you to override it with:

\DefineBibliographyStrings{english}{%
  and = {as well as}%
}

Note:

The format definition for the \textcite context is just the original definition of \finalnamedelim. You might therefore be tempted to try to simply it:

\DeclareDelimFormat[textcite]{finalnamedelim}{\finalnamedelim}

What this actually does is use our format definition for the global context, and so you will get an ampersand, not \bibstring{and}. Incidentally, that is why you can't do this:

\DeclareDelimFormat{finalnamedelim}{\finalnamedelim}

This will send the compiler into an infinite recursion, and it will eventually crash.