Idealism:  In philosophy: Thesis to the effect that everything that exists consists of and arises from the properties, states and relations of ideas.

The strong point of idealism is that it is a philosophy - of which there are quite a few varieties - that is stated in terms of experience: Everything is, somehow, the result of being thought, felt or experienced, if not by human beings or by inanimate things (which also feel and desire, according to many varieities of idealism, albeit in a primitive way) then by God. 'To be is to be perceived', as Berkeley claimed, if only by the mind of God.

The weak point is that idealism has not produced much or any real empirical science of nature, and that empirical science arose from attempts to explain reality and our experiences of it in terms of the properties and relations of material things.

A sort of logical point for idealism is that human beings cannot know anything except what is part of and belongs to their own experience: Anything one comes to believe or think of will always be, whatever its import and truth, some form of one's own experience.

This argument misses or refuses to admit that one can represent things one cannot experience, and find experimental evidence that such things exist nevertheless, even though they may be so small (atoms), or large (the whole universe) or long ago (the Big Bang), or far away in the future (the heath-death of the universe) that one cannot experience them - rather as one can represent a whole country on paper by a map (a piece of paper with a picture) that itself is part of the country, or never came close to it.

A good case of a materialist hypothesis that seemed nonsense from an idealist point of view for ages and yet seems very well supported by modern science is the hypothesis of atoms, that was originally made some 500 years B.C. by Democritus and Leucippus of Abdera, and that nowadays, if not precisely in the same form, is the foundation of much physics and a lot of technology derived from that.

The argument for idealism from experience also misses that in fact nearly all human beings assume that other human beings have experiences like they have. (See: Other minds, Qualia, Personalism)

The strong point of idealism is that so far there is no good materialist explanation of experience - but then the human brain is the most complicated organ known by man. (See: Brain, Qualia)