latter being a tone that rises to a medium level before falling again. It is normally safe to distinguish only between the two tones because there are very few minimal pairs that differ only because of contour. The difference occurs only in certain words ending in the sounds [m] or [ŋ]; for instance, the word kham (, "piece") is pronounced with a high flat tone, whereas the word Khams (, "the Kham region") is pronounced with a high falling tone. In polysyllabic words, tone is not important except in the first syllable. This means that from the point of view of phonological typology, Tibetan could more accurately be described as a pitch-accent language than a true tone language, in the latter of which all syllables in a word can carry their own tone. Consonants In the low tone, the unaspirated are voiced , whereas the aspirated stops and affricates lose some of their aspiration. Thus, in this context, the main distinction between and is voicing. The dialect of the upper social strata in Lhasa does not use voiced stops and affricates in the low tone. The alveolar trill () is in complementary distribution of the alveolar approximant ; therefore, both are treated as one phoneme. The voiceless alveolar lateral approximant resembles the voiceless alveolar lateral fricative found in languages such as Welsh and Zulu and is sometimes transcribed . The consonants , , , , , and may appear in syllable-final positions. The Classical Tibetan final is still present, but its modern pronunciation is normally realized as a nasalisation of the preceding vowel, rather than as a discrete consonant (see above). However, is not pronounced in the final position of a word except in very formal speech. Also, syllable-final and are often not clearly pronounced but realized as a lengthening of the preceding vowel. The phonemic glottal stop appears only at the end of words in the place of , , or , which were pronounced in Classical Tibetan but have since been elided. For instance, the word for Tibet itself was Bod in Classical Tibetan but is now pronounced in the Lhasa dialect. Verbal system The Lhasa Tibetan verbal system distinguishes four tenses and three evidential moods. The three moods may all occur with all three grammatical persons, though early descriptions associated the personal modal category with European first-person agreement. Counting system Lhasa Tibetan has a base-10 counting system.