Origins
The word 'this' is the primary proximal demonstrative in English, used to point at what is near the speaker in space, time, or discourse. It descends from Old English 'þis,' the neuter nominative and accusative form of the demonstrative pronoun 'þes' (this). The Old English paradigm was fully inflected across three genders and five cases: masculine 'þes,' feminine 'þēos,' neuter 'þis,' with distinct forms for genitive, dative, accusative, and instrumental. The neuter nominative 'þis' eventually replaced all other forms during the Middle English period, as grammatical gender collapsed across the language.
The Proto-Germanic ancestor is reconstructed as *þat-si, a compound of the demonstrative base *þat (that, the one) and the deictic particle *-si, which marked proximity to the speaker. This formation reveals the fundamental logic of Germanic demonstratives: 'that' is the unmarked, distal form, while 'this' is 'that + here,' the marked proximal form. The contrast between 'this' and 'that' is not between two independent words but between a base and a derived form — 'this' literally means 'that-here.'
The PIE root underlying the demonstrative base is *tó- (that, the one), one of the most prolific roots in the family. It produced the definite article 'the' (from Old English 'þē,' originally the instrumental case of the demonstrative), 'that' (from Old English 'þæt,' the neuter demonstrative), 'there' (from *þar, in that place), 'then' (from *þan, at that time), 'than' (originally the same word as 'then,' used in comparative constructions), and 'though' (from *þauh, despite that). The initial 'th-' /ð/ in all these words is the Modern English reflex of Old English 'þ' (thorn), which represents the Proto-Germanic *þ from PIE *t — the same sound shift described by Grimm's Law.