CREATE TABLE table_18241 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

Who were the candidates when Jack Fields was the incumbent?
SELECT "Candidates" FROM table_18241 WHERE "Incumbent" = 'Jack Fields'
SELECT "Candidates" FROM "table_18241" WHERE "Incumbent" = 'Jack Fields'