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The goal of the present study was to explore the emergence of verbal behavior resulting from the joint control of two antecedent stimuli that are presented together for the first time. Conditional discriminations were used for teaching and for probing. Four stimuli P1, P2, 01, and 02 were samples and four stimuli A 1, A2, 81 , and 82 were the comparisons in all discriminations of the study. We taught 4 conditional discriminations with 1 sample and 2 comparisons in each trial; overall, each sample controlled selections of 2 comparison stimuli (i.e., sample P1 controlled selections of A1 in 1 conditional discrimination and controlled selections of 81 in another conditional discrimination). In a probe with no reinforcement, 1 P and 1 0 stimuli formed a compound sample, and the 4 comparisons appeared in each trial. Only selections of 1 comparison have been reinforced in the presence of the 2 sample stimuli during teaching (i.e., only selections of A 1 have been reinforced in the presence of P1, in 1 conditional discrimination, and in the presence of 01, in the other conditional discrimination). We analyzed whether the 2 sample stimuli would jointly control comparison selections. In Study 1,2 adult participants did not show the emergence of the discrimination with the compound samples. In Study 2, we modified the procedure of Study 1 in such a way that (a) a prompt procedure was used, (b) trials of the 4 single-sample conditional discriminations were gradually intermixed, and (c) the reinforcement was reduced. The 2 adult participants showed the emergence of the conditional discrimination with the compound samples. This study thus demonstrated the emergence of discriminations by joint control. These results have important consequences for the study of language.