Let’s begin with perception. I experience the physical world though my five senses: sight, taste, touch, hearing, and smell. I do not possess a special “tree-sensing” sense. So how can I experience a tree? The answer is I do not directly experience the tree. — Art48

An abstract object is defined as something which is neither spatial nor temporal: an abstract object does not exist in space and time. (“Object” should not be taken too literally; think “abstract entity.”) A typical example of abstract objects is numbers. Numbers such as 2 or π do not exist in space/time. Yes, two apples exist in a particular place at a particular time; but the number 2 itself does not. — Art48

We can directly see on only one thing: light. The mind does the rest. Almost everything we experience though our senses are universals, are abstract objects, are ideas in our mind. — Art48

My mind directly experiences the number two because the number two is a thought and my mind experiences thoughts directly. Similarly, my mind can directly experience the abstract object named “tree” because that, too, is a thought. As to what is causing my experiences, I suppose there’s a material object, a material tree, existing in a physical universe outside myself. If I’m not dreaming, hallucinating, or a brain in a vat, then my supposition may be correct. There may actually be a material tree, existing in a physical universe outside myself. But, then again, there might not. — Art48

If nearly all the words found in the dictionary stand for abstract objects, then it follows that our experience consists almost exclusively of abstract objects, as I’ll show. — Art48

So how can I experience a tree? The answer is I do not directly experience the tree. — Art48

We can directly see on only one thing: light. The mind does the rest. — Art48

A “brain in a vat” experiences rough brown patches and smooth green patches. Of that experience the brain can be absolutely certain. The brain naturally supposes something in the physical universe called a “tree” is the cause of what we experience. It is wrong. — Art48

My mind directly experiences the number two because the number two is a thought and my mind experiences thoughts directly. Similarly, my mind can directly experience the abstract object named “tree” because that, too, is a thought. As to what is causing my experiences, I suppose there’s a material object, a material tree, existing in a physical universe outside myself. If I’m not dreaming, hallucinating, or a brain in a vat, then my supposition may be correct. There may actually be a material tree, existing in a physical universe outside myself. But, then again, there might not. — Art48

Instead of questioning the existence of abstract object, perhaps we should apply our skepticism the existence of an exterior physical universe. — Art48

Let’s begin with perception. I experience the physical world though my five senses: sight, taste, touch, hearing, and smell. I do not possess a special “tree-sensing” sense. So how can I experience a tree? The answer is I do not directly experience the tree. Rather, my eyes see patches of brown and green; my fingers tell me the brown patches are rough and the green patches are smooth. My mind retrieves the idea “tree” to explain what my senses are telling me. Tree is a mental representation which describes what I experience. (We may suppose a newborn infant only sees patches of light. Over time, the infant deduces the ideas of object, object permanence, and eventually tree.) — Art48

I experience the physical world though my five senses: sight, taste, touch, hearing, and smell. I do not possess a special “tree-sensing” sense. So how can I experience a tree? The answer is I do not directly experience the tree. Rather, my eyes see patches of brown and green; my fingers tell me the brown patches are rough and the green patches are smooth. My mind retrieves the idea “tree” to explain what my senses are telling me. Tree is a mental representation which describes what I experience. (We may suppose a newborn infant only sees patches of light. Over time, the infant deduces the ideas of object, object permanence, and eventually tree.) — Art48

An abstract object is defined as something which is neither spatial nor temporal: an abstract object does not exist in space and time. — Art48

I have no further comment on abstract objects, but I do have something to say about all these purported "illusions" the mind creates. . . . Secondly, the generalization from such "illusions" is dubious - — Agent Smith

This way however, we may at least indirectly experience an abstract tree - through experience of concrete objects and their concrete causal associations in the brain. — litewave

Our five physical senses limit us to experiencing sight, sound, taste, touch, and smell. So, we don’t directly experience concrete objects. — Art48

What could this mean “we don’t directly experience concrete objects” I see a tree, I go over to touch the leaves, smell the bark, hear the creaking of the branches, or taste the fruit it produces. How more direct can we get? — Richard B

Austin's criticism of "universal" concepts starts at about p.84. — Banno

As a matter of fact, if any one were anxious to deny altogether that there are such things as universals, we should find that we cannot strictly prove that there are such entities as qualities, i.e. the universals represented by adjectives and substantives, whereas we can prove that there must be relations, i.e. the sort of universals generally represented by verbs and prepositions.

Let us take in illustration the universal whiteness. If we believe that there is such a universal, we shall say that things are white because they have the quality of whiteness. This view, however, was strenuously denied by Berkeley and Hume, who have been followed in this by later empiricists. The form which their denial took was to deny that there are such things as 'abstract ideas '. When we want to think of whiteness, they said, we form an image of some particular white thing, and reason concerning this particular, taking care not to deduce anything concerning it which we cannot see to be equally true of any other white thing. As an account of our actual mental processes, this is no doubt largely true. In geometry, for example, when we wish to prove something about all triangles, we draw a particular triangle and reason about it, taking care not to use any characteristic which it does not share with other triangles. The beginner, in order to avoid error, often finds it useful to draw several triangles, as unlike each other as possible, in order to make sure that his reasoning is equally applicable to all of them.

But a difficulty emerges as soon as we ask ourselves how we know that a thing is white or a triangle. If we wish to avoid the universals whiteness and triangularity, we shall choose some particular patch of white or some particular triangle, and say that anything is white or a triangle if it has the right sort of resemblance to our chosen particular. But then the resemblance required will have to be a universal. Since there are many white things, the resemblance must hold between many pairs of particular white things; and this is the characteristic of a universal. It will be useless to say that there is a different resemblance for each pair, for then we shall have to say that these resemblances resemble each other, and thus at last we shall be forced to admit resemblance as a universal. The relation of resemblance, therefore, must be a true universal. And having been forced to admit this universal, we find that it is no longer worth while to invent difficult and unplausible theories to avoid the admission of such universals as whiteness and triangularity. ...

It is largely the very peculiar kind of being that belongs to universals which has led many people to suppose that they are really mental. We can think of a universal, and our thinking then exists in a perfectly ordinary sense, like any other mental act. Suppose, for example, that we are thinking of whiteness. Then in one sense it may be said that whiteness is 'in our mind'. ... In the strict sense, it is not whiteness that is in our mind, but the act of thinking of whiteness. The connected ambiguity in the word 'idea', which we noted at the same time, also causes confusion here. In one sense of this word, namely the sense in which it denotes the object of an act of thought, whiteness is an 'idea'.

Hence, if the ambiguity is not guarded against, we may come to think that whiteness is an 'idea' in the other sense, i.e. an act of thought; and thus we come to think that whiteness is mental. But in so thinking, we rob it of its essential quality of universality. One man's act of thought is necessarily a different thing from another man's; one man's act of thought at one time is necessarily a different thing from the same man's act of thought at another time. Hence, if whiteness were the thought as opposed to its object, no two different men could think of it, and no one man could think of it twice. That which many different thoughts of whiteness have in common is their object, and this object is different from all of them. Thus universals are not thoughts, though when known they are the objects of thoughts. — Bertrand Russell, World of Universals

Consider that when you think about triangularity, as you might when proving a geometrical theorem, it is necessarily perfect triangularity that you are contemplating, not some mere approximation of it. Triangularity as your intellect grasps it is entirely determinate or exact; for example, what you grasp is the notion of a closed plane figure with three perfectly straight sides, rather than that of something which may or may not have straight sides or which may or may not be closed. Of course, your mental image of a triangle might not be exact, but rather indeterminate and fuzzy. But to grasp something with the intellect is not the same as to form a mental image of it. For any mental image of a triangle is necessarily going to be of an isosceles triangle specifically, or of a scalene one, or an equilateral one; but the concept of triangularity that your intellect grasps applies to all triangles alike. Any mental image of a triangle is going to have certain features, such as a particular color, that are no part of the concept of triangularity in general. A mental image is something private and subjective, while the concept of triangularity is objective and grasped by many minds at once. — Edward Feser

We shall find it convenient only to speak of things existing when they are in time, that is to say, when we can point to some time at which they exist (not excluding the possibility of their existing at all times). Thus thoughts and feelings, minds and physical objects exist. But universals do not exist in this sense; we shall say that they subsist or have being, where 'being' is opposed to 'existence' as being timeless. The world of universals, therefore, may also be described as the world of being. — Russell, World of Universals

Instead of questioning the existence of abstract object, perhaps we should apply our skepticism the existence of an exterior physical universe. — Art48

Bowdlerising his argument, it simply is not the case that the grey of a cloud and the grey of this laptop have something in common - apart from our use of the word "grey". — Banno

Bowdlerising his argument, it simply is not the case that the grey of a cloud and the grey of this laptop have something in common - apart from our use of the word "grey". Or if you prefer, abstract objects do not exist. — Banno