From a grammar point of view, the role of punctuation marks in a sentence is formally
define
d an
d well un
derstoo
d. In semantic analysis punctuation plays also a crucial role as a metho
d of avoi
ding ambiguity of the meaning. A
different situation can be observe
d in the statistical analyses of language samples, where the
decision on whether the punctuation marks shoul
d be consi
dere
d or shoul
d be neglecte
d is seen rather as arbitrary an
d at present it belongs to a researcher’s preference. An objective of this work is to she
d some light onto this problem by provi
ding us with an answer to the question whether the punctuation marks may be treate
d as or
dinary wor
ds an
d whether they shoul
d be inclu
de
d in any analysis of the wor
d co-occurrences. We alrea
dy know from our previous stu
dy (S. Dro
żdż et al., Inf. Sci. 331 (2016) 32-44) that full stops that
determine the length of sentences are the main carrier of long-range correlations. Now we exten
d that stu
dy an
d analyse statistical properties of the most common punctuation marks in a few In
do-European languages, investigate their frequencies, an
d locate them accor
dingly in the Zipf rank-frequency plots as well as stu
dy their role in the wor
d-a
djacency networks. We show that, from a statistical viewpoint, the punctuation marks reveal properties that are qualitatively similar to the properties of the most frequent wor
ds like articles, conjunctions, pronouns, an
d prepositions. This refers to both the Zipfian analysis an
d the network analysis. By a
dding the punctuation marks to the Zipf plots, we also show that these plots that are normally
describe
d by the Zipf&n
dash;Man
delbrot
distribution largely restore the power-law Zipfian behaviour for the most frequent items.
d="spara0002">Our results indicate that the punctuation marks can fruitfully be considered in the linguistic studies as their inclusion effectively extends dimensionality of an analysis and, therefore, it opens more space for possible manifestation of some previously unobserved effects.