\section{Conclusion}
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We have shown in this paper that languages can and do employ 
various ways of encoding dependencies: either by imposing 
word order, or by introducing special markers, which are 
called agreement markers or case markers, depending on the 
way they function in the syntax. These encodings are called 
{\it regimes}. There are two regimes which can stand alone in 
the sense that each sentence is unambiguous. These are  
the so--called Polish Notation (and its reverse image) 
and the case marking regime which is consistently word marking. 
For the positional regimes, Montague has defined a semantics 
that allows a compositional syntax--to--meaning translation. 
We have provided a semantics for the case marking languages. 
This semantics gives correct results for peripheral group 
marking languages as well as word marking languages, and so 
is quite flexible. Notice that neither Montague Semantics
nor the semantics we have proposed here rely on the unambiguity 
of the language. Rather, they will predict that sentences 
can and must be ambiguous if the semantic mapping yields 
several distinct meanings, each corresponding to a different 
parse of that sentence. However, we have excluded that 
question from our discussion. In this way it was easier 
to motivate the usefulness of the various regimes. 

This motivation can of course work only if one accepts the 
thesis that languages strive to make their sentences unambiguous. 
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\footnote{A note of clarification is perhaps in order. It 
might be undisputed that speakers strive to make their sentences 
unambiguous. (This is one of Grice's maxims!) Since speakers can 
normally take the context into account, they might not always 
produce fully unambiguous sentences, and --- as one learns --- 
many sentences are ambiguous at closer look (see 
Altman~\cite{altmann:babel}). Yet, there are certain basic 
ambiguities that must in general be avoided, such as a potential 
confusion between subject and object ({\it John pestered Peter\/} 
versus {\it Peter pestered John\/}). If that is accepted, then it 
is clear that speakers will tend not to use those kinds of 
constructions that are 
ambiguous. Initially, these constructions might still be grammatical, 
but the less they are used the less grammatical they appear. In the end, 
they will be judged ungrammatical, and then we say that the language 
has changed. For example, scrambling in German can yield sentences 
that are disfavoured for precisely the reason that they appear to 
be SOV but are intended as OSV. We predict therefore that German 
moves in direction of a language in which scrambling of the direct 
object is prohibited. In this way, pragmatic principles can bear 
on the question of language, and we can attribute to language 
roughly the same tendencies as to individual speakers.} 
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This therefore comes down to claiming that avoiding ambiguity is 
a motor of language change. However, this works canonically only in 
one direction. Namely, when the morphology becomes unable to make 
enough distinctions, the languages tend to become more rigorous 
with word order. When the language develops some kind of marking 
mechanism, although it might afford to loosen the positional regime, 
this need not happen. A particularly outspoken proponent of this idea 
is Vennemann (see, for example, \cite{vennemann:drift}).
His claim is that languages with basic SOV order become SVO 
when the morphological distinctions between subject and object 
disappear as a consequence of the gradual morphological attrition. 
This is attested for virtually all Indo--European languages, 
for example. (See for example \cite{lehmann:compound} for the 
development of Proto--IE to Late IE.) Now, while Vennemann's 
thesis is rather specific in the conditions and directions of 
change --- he does not consider free word languages and the result 
is a specific regime that appears to be less than optimal from our 
results --- he nevertheless emphasizes that it is the resulting ambiguity 
of sentences that motivates the change. It is worth a separate 
study why SVO languages are actually better suited than 
SOV languages. We shall briefly discuss some of the reasons. An 
interesting one 
is that question words and relativizers are clause initial 
and so a transitive question or relative clause would necessarily 
be ambiguous. Of course, it is not logically necessary for the 
question word or the relativizer to be clause initial, and this 
in turn means that the direction of language change depends in 
part on other characteristics of language. These might 
be universal or accidental, which means that Vennemann's thesis 
may actually be false in general should it turn out that some 
of the characteristics are not universal. But this has not been 
the topic of the present paper. What we were interested in are the 
formal (and therefore inescapable) consequences of particular 
languagae characteristics, in order to provide the background for 
such theories as those of Vennemann's. 

The model presented in this paper is however still too simplistic. 
Even though there are languages which are consistently word 
marking, they do not match the theoretical model in cases of 
modification and coordination. A modifier does not case mark 
its argument, neither does a coordinator. It follows therefore 
that even the consistently word marking languages must have 
certain positional regimes or else a different semantic mapping 
algorithm must be found. This question needs investigation. 
