Through experience, experimentation, and observation, psychologists can predict human behaviors much in the same way that scientists in other fields can predict outcomes based on their findings. Knowledge about human behavior is based on general experience. A psychologist can recall memories and events from their own interactions with other people, and use the information to predict behaviors in patients and test subjects. They can also simply "people watch" to observe people in everyday situations. Psychologists devise experiments to observe how people react to a given situation. The outcomes of these experiments can inform psychologists of behavioral patterns. These findings can be used to predict human behaviors in the same or similar situations. Psychology is therefore a science because the body of knowledge it builds can be used to predict human behaviors.
Although valuable insights can be gleaned from observing people, the findings are unreliable at best due to humans' unpredictable nature. A psychologist can make general assumptions about how a person might react in a given situation, but there is no guarantee that every person will react in the same way. Observing people through controlled experiments is also unreliable, because it would be difficult to replicate the ideal setting and situation of an experiment out in the real world, and vice versa. A person might behave differently during an experiment in which they are being observed as opposed to facing the same situation in real life. These findings are not very useful in predicting human behaviors. Psychology can't be considered a science if its entire base of knowledge is muddled with such inconsistencies.
[P1] Psychology is a science because it uses experience, experimentation, and observation to record, analyze, and predict human behaviors.
Rejecting the premises
[Rejecting P1] Psychology can't be considered a science because its body of knowledge is unreliable at making accurate predictions about human behavior.