There are two types of arguments: deductive and inductive. In a deductive argument, provided the premises are true, the conclusion is certainly true. For example: All ducks are birds (premise). Daffy is a duck (premise). Therefore, Daffy is a bird (conclusion). Deductive arguments are used by rationalists, because they use reason rather than experience, and provide certainty rather than probability. Deductive arguments are most used in the field of mathematics.
An inductive argument is constructed in such a way that if the premises are true, it is probable that the conclusion is true as well. For example: Most birds can fly. Daffy is a bird. Therefore, Daffy can fly. In this, it is probable that the conclusion is true, but not certain. Inductive arguments use reasoning based on what has been observed. For example: Pots of water are generally observed to boil at 100 degrees centigrade, therefore water boils as 100 degrees centigrade. This is not certain, because there could be an unobserved pot of water that has boiled at a different temperature. Most fields besides mathematics make use of inductive arguments.
While deductive arguments are always certain, they are flawed in that they don’t obtain any new information. The conclusion is always contained implicitly in the premises. At best, deductive arguments merely uncover truths that were just unrecognised or obscured previously. Certainty comes at a cost.
Inductive arguments (favoured by empiricists such as my fine self) while marred with the threat of falsehood, provide new knowledge and expand our understanding of the world in ways deduction never could.