This thesis investigates the implications of positive polarity for grammar. The empirical focus is on two positive polarity particles in Sinhala, an Indo-Aryan language spoken in Sri Lanka. Sinhala has two particles -hari and -da that systematically appear across disjunction, indefinite and question constructions. Traditionally, these particles have been called Q-particles (i.e. Hagstrom (1998); Cable (2010); Slade (2011); a.m.o). They have so far been analyzed in terms of either Q-question/-uantifier operators (Kishimoto (2005)) or choice function variables (cf. Hagstrom (1998); Cable (2010); Slade (2011)). This thesis presents new data pertaining to the distribution and interpretation of disjunctions and indefinites formed with the two particles in contexts of negation, modals, quantifiers and intensional operators, that none of the previous accounts has captured. It proposes to analyze the grammar of the two particles based on their positive polarity character associated with exhaustivity (cf. Spector (2014); Nicolae (2017)). It claims that we can account for a wide range of grammatical phenomena such as ignorance inferences, scope or non/specificity effects, free/no choice implicatures and de re/dicto readings of -hari and -da disjunctions/indefinites in matrix and overt modal/quantifier contexts based on a distribution requirement (DR) derived by way of exhaustification with respect to alternatives of a disjunction or indefinite. The thesis casts its proposal in a hybrid system of lexical (cf. Levinson (2000); Chierchia (2004)) and grammatical (cf. Fox (2007); Chierchia et al. (2012)) approaches borrowing insights from both approaches. It also utilizes a hybrid framework of Hamblin semantics (cf. Hamblin (1973); Kratzer and Shimoyama (2002); Alonso-Ovalle (2006)) to keep domain alternatives separated and application of an alternative sensitive exhaustivity (Exh) operator (cf. the grammatical approach) to derive implicatures. Obligatory exhaustivity is treated as a morphological requirement/ lexical property of the particles -hari and -da represented by an uninterpretable exhaustivity [unExh] feature. Then, this lexical property is factored into the grammar by way of the Exh operator carrying an equivalent interpretable exhaustivity [inExh] feature placed in the syntactic structure of a -hari and -da disjunction/indefinite construction at LF. “Inclusivity” and “exclusivity” components of the particles -hari and -da that have consequences for distribution requirements are derived by way of different morpho-syntactic requirements of the particles -hari and -da. Thus, this thesis proposes a fully compositional/grammatical account all the way from the bottom to the top in the derivations.