\uppercase command does not work with greek characters

Question

MWE:

\documentclass[a4paper,12pt]{report}

\usepackage{geometry}

\usepackage[LGR,T1]{fontenc}
\usepackage[utf8]{inputenx}
\usepackage[english,greek]{babel}

\begin{document}

\selectlanguage{english}
\uppercase{\textgreek{τα κεφαλαία δεν δουλεύουν}}

\selectlanguage{greek}
\uppercase{τα κεφαλαία δεν δουλεύουν}

\end{document}

Output:

As it can be seen the \uppercase command doesn't seem to work with greek characters, or it seems to work partly.

Answer 1

You should use \MakeUppercase instead of \uppercase:

\documentclass[a4paper,12pt]{report}

\usepackage{geometry}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenx}
\usepackage[english,greek]{babel}

\begin{document}

\selectlanguage{english}
\uppercase{\textgreek{τα κεφαλαία δεν δουλεύουν}}

\selectlanguage{greek}
\uppercase{τα κεφαλαία δεν δουλεύουν}

\MakeUppercase{τα κεφαλαία δεν δουλεύουν}

\end{document}

Answer 2

To complement Christian’s answer, let me recall what \uppercase does.

When you do \uppercase{<text>}, the characters in <text> (as opposed to commands) are converted to their uppercase equivalent as established by a vector loaded into memory.

For example, a will turn into A, because the vector contains, at the slot 0x61 the value 0x41; on the other hand commas and so on will not change, because in the corresponding slots the vector has 0 (which is the marker telling TeX not to change the character).

Now, for LaTeX, a tau is not a single character, but two (due to UTF-8), precisely the characters in slots 0xCF and 0x84 (hexadecimal).

Here is the correspondence table when LaTeX starts up:

80->80    81->81    82->82    83->83    84->84    85->85    86->86    87->87
88->88    89->89    8A->8A    8B->8B    8C->8C    8D->8D    8E->8E    8F->8F

90->90    91->91    92->92    93->93    94->94    95->95    96->96    97->97
98->98    99->99    9A->9A    9B->9B    9C->9C    9D->9D    9E->D0    9F->0

A0->80    A1->81    A2->82    A3->83    A4->84    A5->85    A6->86    A7->87
A8->88    A9->89    AA->8A    AB->8B    AC->8C    AD->8D    AE->8E    AF->8F

B0->90    B1->91    B2->92    B3->93    B4->94    B5->95    B6->96    B7->97
B8->98    B9->99    BA->9A    BB->9B    BC->9C    BD->0     BE->0     BF->0

C0->C0    C1->C1    C2->C2    C3->C3    C4->C4    C5->C5    C6->C6    C7->C7
C8->C8    C9->C9    CA->CA    CB->CB    CC->CC    CD->CD    CE->CE    CF->CF

D0->D0    D1->D1    D2->D2    D3->D3    D4->D4    D5->D5    D6->D6    D7->D7
D8->D8    D9->D9    DA->DA    DB->DB    DC->DC    DD->DD    DE->DE    DF->DF

E0->C0    E1->C1    E2->C2    E3->C3    E4->C4    E5->C5    E6->C6    E7->C7
E8->C8    E9->C9    EA->CA    EB->CB    EC->CC    ED->CD    EE->CE    EF->CF

F0->D0    F1->D1    F2->D2    F3->D3    F4->D4    F5->D5    F6->D6    F7->D7
F8->D8    F9->D9    FA->DA    FB->DB    FC->DC    FD->DD    FE->DE    FF->DF

(just the characters beyond 0x7F are shown here). There are reasons behind these values, but it would take too long to explain them.

Anyway, you see that 0xCF and 0x84 don't change, so a tau will remain unchanged. On the other hand a kappa is input as 0xCE and 0xBA; the first part doesn't change, the second one becomes 0x9A and the combination 0xCE followed by 0x9A in UTF-8 is indeed an uppercase Greek kappa.

There's no way this can work for every UTF-8 character; moreover, control sequences would remain the same, which would be a nuisance for other languages (for instance, in German \ss should become \SS, for proper output).

Thus LaTeX has introduced \MakeUppercase that “does the right thing”, using \uppercase in some cases, a different conversion table in others.

Similarly, \lowercase should not be used in LaTeX: the correct command is \MakeLowercase.