Analytic and synthetic are two different kinds of truths.
- Analytic truth: true in virtue of the meaning of the words
- E.g. “A bachelor is an unmarried man”, or, “triangles have three sides”
- Synthetic truth: true in virtue of how the world is
- E.g. “Grass is green”, or, “water boils at 100°c”
Analytic truths cannot be denied without resulting in a logical contradiction. To say, “not all bachelors are unmarried”, for example, is to misunderstand the word bachelor – the concept of a married bachelor does not make sense. Similarly, one cannot coherently imagine a triangle with four sides because the very idea involves a contradiction.
Denial of a synthetic truth does not lead to a logical contradiction. For example, we can coherently imagine red grass in denial of the synthetic truth “grass is green”. Though experience tells us grass is not, in fact, red, there is no logical contradiction in this idea.
The distinction between necessary and contingent truths is very similar to the distinction between analytic and synthetic truths:
- Necessary truths must be true (so are more or less analytic truths)
- E.g. “Triangles have three sides”
- Contingent truths might not have been true (so are more or less synthetic truths)
- E.g. “Toblerone is a triangle shape”
A priori and a posteriori are two different kinds of knowledge:
- A priori knowledge: knowledge that can be acquired without experience of the external world, through thought alone
- E.g. working out what 900 divided by 7 is
- A posteriori knowledge: knowledge that can only be acquired from experience of the external world
- E.g. doing an experiment to discover the temperature at which water boils
Most a priori knowledge is knowledge of analytic truths and most a posteriori knowledge is knowledge of synthetic truths. The disagreement between rationalism and empiricism is whether this relationship holds in all cases, or whether there are exceptions:
- Rationalism says there are some synthetic truths that can be known a priori.
- Empiricism says all knowledge of synthetic truths is acquired a posteriori.
In other words, empiricism says there is no such thing as synthetic a priori knowledge and rationalism says there is at least one synthetic truth that is known a priori.
Qualia are the subjective qualities of experience – i.e. what something feels like inside your mind. Qualia are not properties of objects, but properties of minds/experience. Examples of qualia include:
- The redness I experience when I look at a ripe tomato
- The taste of beer when I have a drink
- The rough feeling when I run my hand over some sandpaper
Knowledge of qualia is sometimes called phenomenal knowledge – i.e. knowledge of what it is like to have a certain experience.