In astrology, a hard aspect is an astrological aspect that stimulates the native to take some action to resolve tension, conflict, or stress in his life. Because they required the native to take action, they are very motivational in nature. All hard aspects are considered to be disharmonious on some level because an easy flow of energy does not exist within them. The conjunction and the parallel are sometimes considered to be hard because they stimulate action, but they are not always disharmonious because quite often the activities they induce can bring about positive outcomes.
When determining whether an aspect is disharmonious, therefore, one would need to look at the planets involved and see the influence they play in the situation. An example of this would be the planet Pluto. Because of the extreme nature of the planetoid, just about any aspect it makes is going to be considered hard because it forces the native to look closely at his life, make appropriate changes, or risk losing that which is important to him. Therefore, even though the trine and sextile are considered to be easy aspects, any aspect they make with Pluto is likely to be fraught with difficulties until the native learns to transform his environment through the transcendental nature of the planet.
In financial astrology the hard aspect is deemed to make it hard for the stock and currency markets to go up, and easier for them to go down. Whilst soft aspects have the opposite effect. Then there are periods that there are none of the exact major aspects, and the stock and currency markets remain flat.
The aspects that are considered to be hard are the semi-square, square, sesquiquadrate and opposition.