that
conj.conj. a word used to connect a main part of a sentence to a new clause that adds more information. You use it to introduce what someone says, thinks, or feels.
conj. introduces a subordinate clause that functions as the object or complement of a verb, adjective, or noun. Often omitted in informal spoken registers when the meaning remains clear.
I hope that you have a great day.
The scientist argued that the new data would change how we understand the history of the planet.
The prevailing philosophical consensus suggests that human consciousness is not a singular entity but rather a complex series of interconnected cognitive processes occurring simultaneously.
From Middle English that, from Old English þæt (“the, that”, neuter definite article and relative pronoun), from Proto-West Germanic þat, from Proto-Germanic þat. Cognate to Scots that, Saterland Frisian dät, West Frisian dat, Dutch dat, Low German dat and datt, German dass and das, Danish det, Swedish det, Icelandic það, Gothic 𐌸𐌰𐍄𐌰 (þata). Further from Proto-Indo-European *tód; compare Ancient Greek τό (tó), Sanskrit तद् (tád), Waigali ta, Lithuanian tai̇̃, Polish to.
Often functions as a complementizer; it can be omitted in informal contexts ('I think that it's raining' vs 'I think it's raining').
He told that he was tiredHe said that he was tiredThe verb 'tell' requires a personal object (e.g., 'He told me that...') whereas 'say' can be followed directly by a 'that' clause.