There are two main theories about the origin of this word. Both derived the first syllable from Proto-Baltic *ta-, from Proto-Indo-European *to-, an old pronominal stem, whence also tas (“this”). The second syllable is, according to one theory, from the particle ga and an extra -d (< da). The same particle ga can be found in Lithuanian tàgatės (“thus, like that”) and Old Prussian anga (“or”), and in reduced form in 17th-century arīg (modern arī “too”) and as dz (< *dzi < parallel form *gi) in nedz). An alternative theory, however, derives the second syllable in tagad from gads, now “year” but previously also “time”: from an earlier accusative *tagadi (“this time”) would have come present-day tagad “now.” Cognates include Old Church Slavonic тогда (togda), тъгда (tŭgda), Russian тогда́ (togdá), Ukrainian тогді́ (tohdí), тогі́д (tohíd, “last year”), Bulgarian тога́ (togá), Czech tehdy, dialectal tehda (“then”).