Trine
A trine is two bodies 120 degrees apart, in signs of the same element, and it is the easiest of the five major aspects: the two planets agree without effort.
Because the signs share an element they share the underlying qualities, so the planets in a trine cooperate by temperament rather than by negotiation. Fire trines fire, water trines water.
The classical caution about trines is not that they are weak but that they are unforced. What comes easily is rarely worked at, and a talent that never met resistance can stay undeveloped. Ancient authors call the trine fortunate; they do not call it productive.
Frequently asked
Is a trine always good?
It is always easy, which is not the same thing. Two difficult planets in trine cooperate smoothly at whatever they are doing.
What is a grand trine?
Three planets each trine the other two, forming a closed triangle in one element. It concentrates the ease and the risk of it.